serious illness — bad illness
collocationB1IELTS 5+neutralcommon
An illness that is severe, dangerous, or could have major effects on your health.
Say it like a native
Textbook He is suffering from a grave medical condition.
Native He's got a serious illness.
'A serious illness' is the everyday phrase; 'a grave medical condition' is clinical/report-speak.
Pattern: serious illness (noun phrase); have/suffer from/develop a serious illness
In use
- After being diagnosed with a serious illness, she had to spend several weeks in the hospital.health
- If a family member has a serious illness, it can affect everyone’s daily routine and emotional well-being.IELTS speaking
Common mistake
✗ She has a heavy illness.
✓ She has a serious illness.
Illnesses are 'serious', not 'heavy' (heavy is about weight).
Common collocations
a serious illness— suffer from, develop, recover from, life-threatening
Don't confuse it
Not used for small or minor health problems like a headache or a cold.