Idioms are special expressions in English where the meaning is different from the literal meaning of the words.
For example, when someone says they are “under the weather,” they usually don’t mean the weather is literally affecting them—they mean they feel unwell.
Idioms make everyday English more colorful, expressive, and natural.
Learning idioms related to being sick or feeling unwell is especially useful because health is something people talk about frequently in daily life.
Whether you’re speaking with coworkers, chatting with friends, or writing messages, these expressions help you describe illness in a natural and fluent way.
Many English learners already know basic phrases like “I’m sick” or “I feel ill,” but native speakers often use health-related idioms,
illness expressions, and conversational English phrases instead. Understanding these expressions improves listening skills and helps you communicate more confidently.
In this guide, you’ll learn 12 useful idioms for describing sickness or feeling unwell, along with meanings, real-life examples, and practical tips so you can use them naturally in conversations, writing, and exams.
Quick Overview Table
| Idiom | Short Meaning | Tone | Common Use Context |
|---|---|---|---|
| Under the weather | Feeling slightly sick | Informal | Casual conversation |
| Sick as a dog | Very sick | Informal | Talking to friends |
| Green around the gills | Looking nauseous | Informal | Observing someone ill |
| Run down | Physically exhausted or weak | Neutral | Work or daily life |
| Out of commission | Unable to function due to illness | Neutral | Workplace or daily talk |
| Not feeling oneself | Feeling different due to illness | Neutral | Polite conversation |
| At death’s door | Extremely sick | Dramatic/Informal | Storytelling |
| On one’s last legs | Very weak or exhausted | Informal | Illness or fatigue |
| Take a turn for the worse | Health suddenly declines | Formal/Neutral | Medical or serious context |
| Off color | Slightly ill | Informal | Casual description |
| Under the knife (sometimes illness-related) | Having surgery | Neutral | Medical context |
| Back on one’s feet | Recovered from illness | Neutral | Recovery situations |
Detailed Idioms Section
Under the Weather
Meaning: Feeling slightly sick, tired, or not in good health.
When to Use It: This phrase is commonly used when someone has a mild illness such as a cold, headache, or fatigue.
Example Sentence:
I might skip the meeting today because I’m feeling a bit under the weather.
Similar Expressions: Feeling unwell, a little off
Opposite Expression: In perfect health
Sick as a Dog
Meaning: Extremely ill or suffering from strong sickness.
When to Use It: Used in informal situations to emphasize how badly someone feels.
Example Sentence:
After eating the spoiled seafood, he was sick as a dog all night.
Similar Expressions: Very ill, terribly sick
Opposite Expression: Fit as a fiddle
Green Around the Gills
Meaning: Looking pale or nauseous due to illness.
When to Use It: Used when someone appears visibly sick or about to vomit.
Example Sentence:
You look green around the gills—maybe you should sit down for a while.
Similar Expressions: Looking pale, looking queasy
Opposite Expression: Looking healthy
Run Down
Meaning: Physically exhausted or weakened due to stress, illness, or lack of rest.
When to Use It: Often used when someone’s health declines because they worked too hard.
Example Sentence:
She became run down after working late every night for weeks.
Similar Expressions: Exhausted, worn out
Opposite Expression: Energized
Out of Commission
Meaning: Temporarily unable to work or function due to sickness or injury.
When to Use It: Often used when someone cannot perform normal tasks.
Example Sentence:
My back injury has put me out of commission for a few days.
Similar Expressions: Unable to function, inactive
Opposite Expression: Fully operational
Not Feeling Oneself
Meaning: Feeling physically or mentally different because of illness.
When to Use It: Used in polite conversation when someone doesn’t want to say they are sick directly.
Example Sentence:
I’m not feeling myself today, so I’ll rest at home.
Similar Expressions: Feeling off, not well
Opposite Expression: Feeling great
At Death’s Door
Meaning: Extremely sick or close to dying.
When to Use It: Often used dramatically in stories or serious illness descriptions.
Example Sentence:
He was at death’s door with pneumonia before the doctors saved him.
Similar Expressions: Critically ill, seriously sick
Opposite Expression: Healthy and strong
On One’s Last Legs
Meaning: Extremely weak or near collapse.
When to Use It: Used for both people and things that are about to stop working.
Example Sentence:
After a week of high fever, she felt like she was on her last legs.
Similar Expressions: Barely functioning, extremely weak
Opposite Expression: Full of energy
Take a Turn for the Worse
Meaning: A sudden decline in someone’s health.
When to Use It: Used in serious medical or hospital-related discussions.
Example Sentence:
Unfortunately, his condition took a turn for the worse overnight.
Similar Expressions: Condition deteriorated, health declined
Opposite Expression: Take a turn for the better
Off Color
Meaning: Slightly ill or not feeling normal.
When to Use It: Used when someone looks tired or mildly sick.
Example Sentence:
She seemed a bit off color during the meeting today.
Similar Expressions: Slightly sick, not quite well
Opposite Expression: In great shape
Under the Knife
Meaning: Having surgery or undergoing an operation.
When to Use It: Used when someone needs medical surgery.
Example Sentence:
He will go under the knife tomorrow for his knee surgery.
Similar Expressions: Have surgery, undergo an operation
Opposite Expression: Recovering normally
Back on One’s Feet
Meaning: Fully recovered from illness.
When to Use It: Used when someone has regained health after sickness.
Example Sentence:
After two weeks of rest, she was finally back on her feet.
Similar Expressions: Recovered, healthy again
Opposite Expression: Still sick
Categorizing the Idioms
Idioms for Positive Situations (Recovery)
Back on one’s feet
Take a turn for the better
Fit as a fiddle (related expression)
Idioms for Difficult Situations
Sick as a dog
At death’s door
On one’s last legs
Take a turn for the worse
Funny or Informal Idioms
Under the weather
Green around the gills
Off color
Neutral or Professional Context
Run down
Out of commission
Under the knife
Not feeling oneself
How to Use These Idioms in Real Conversations
Workplace Example
“I’m a little under the weather today, so I’ll finish the report from home.”
Casual Conversation Example
“I was sick as a dog after that street food last night.”
Writing Example (Email)
“Dear Manager,
I’m feeling a bit under the weather today and will be working remotely.”
IELTS or Exam Tip
Using idioms naturally in speaking exams can improve fluency and vocabulary scores. However, use them only when they fit the situation naturally.
Common Mistakes to Avoid
Literal Misunderstanding
Many learners think idioms mean exactly what the words say. For example, “under the weather” does not mean standing in the rain.
Using Informal Idioms in Formal Writing
Expressions like “sick as a dog” are very informal and should not appear in academic essays.
Overusing Idioms
Using too many idioms in one conversation can sound unnatural. Use them sparingly.
Practice Exercises
Fill in the Blanks
- I stayed home because I was feeling ______ the weather.
- After the long illness, she was finally back on her ______.
- He looked green around the ______ during the bus ride.
- The patient suddenly took a turn for the ______.
- After working nonstop, I feel completely ______ down.
- I can’t come to work today—I’m ______ as a dog.
- The surgery means he will go ______ the knife tomorrow.
- My laptop is out of ______ today.
- She said she wasn’t feeling ______ today.
- After the fever, he felt like he was on his last ______.
Multiple Choice
- Which idiom means “slightly sick”?
A) Under the weather
B) At death’s door
C) On one’s last legs - Which idiom means “recovered”?
A) Back on one’s feet
B) Green around the gills
C) Sick as a dog - Which expression means “extremely sick”?
A) Off color
B) Sick as a dog
C) Run down - Which idiom refers to surgery?
A) Under the knife
B) Out of commission
C) Run down - Which phrase means “health suddenly worsened”?
A) Back on one’s feet
B) Take a turn for the worse
C) Off color
Writing Prompts
- Write a short paragraph about a time you felt under the weather.
- Describe someone recovering from illness using two idioms.
- Write a short dialogue using at least three idioms from this guide.
Answers
Fill in the blanks:
- under
- feet
- gills
- worse
- run
- sick
- under
- commission
- oneself
- legs
Multiple Choice:
- A
- A
- B
- A
- B
FAQs
What are idioms for sickness?
Idioms for sickness are figurative expressions used to describe illness or poor health without stating it directly.
Why do native speakers use illness idioms?
They make speech more natural, expressive, and conversational.
Are these idioms appropriate for formal writing?
Most are informal, so they are better suited for conversation rather than academic writing.
How can learners remember idioms easily?
Practice them in conversations, read them in context, and use them in sentences regularly.
Are idioms useful for English exams?
Yes. Using idioms appropriately can improve fluency and vocabulary scores in speaking tests.
Conclusion
Learning idioms related to sickness is a powerful way to sound more natural in English conversations.
Instead of simply saying “I am sick,” expressions like “under the weather,” “run down,” or “back on my feet” add depth and authenticity to your language.
By understanding when and how to use these expressions, you can communicate health situations more clearly and confidently.
Topic-based idioms also improve listening skills because native speakers frequently use them in everyday speech.
The best way to master idioms is through regular exposure and practice. Use them in conversations, writing, and speaking exercises until they become a natural part of your vocabulary.
Over time, these expressions will help you move from basic English to fluent, natural communication.
Corvin Hale is a language enthusiast who makes learning English idioms simple and fun.
