Flu is short for influenza, the contagious illness that causes fever and aches. Flew is the past tense of the verb fly, describing something that moved through the air. A simple hook: flu is a noun you catch, flew is a verb about the past, as in the plane flew overhead.
The core difference
Flu is an illness (short for influenza), while flew is the past tense of the verb fly.
- flu — the everyday name for influenza, a viral bug that leaves you feverish, achy, and worn out: get your flu shot before winter sets in.
- flew — the verb fly, put into the past: something travelled through the air already: the plane flew over the mountains just before sunset.
How to tell them apart
Because flu and flew sound similar in fast speech, the useful check is grammar rather than sound: flu never changes form and never takes an object, while flew is always describing an action that already happened. If a sentence needs a verb in the past tense, it needs flew, not flu.
The mix-up tends to appear in casual writing and texting, where someone means the illness but types flew, or means the verb but types flu. Remembering that flu is simply a shortened form of influenza, with no connection to flying, settles it quickly.
