/ wʌns; NAmE / adverb , conjunction
■ adverb
1.
on one occasion only; one time :
I've only been there once.
He cleans his car once a week.
She only sees her parents once every six months.
( informal )
He only did it the once .
2.
at some time in the past :
I once met your mother.
He once lived in Zambia.
This book was famous once, but nobody reads it today.
3.
used in negative sentences and questions, and after if to mean 'ever' or 'at all' :
He never once offered to help.
If she once decides to do something, you won't change her mind.
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IDIOMS
- all at once
- at once
- (just) for once | just this once
- going once, going twice, sold
- once again | once more
- once a ... , always a ...
- once and for all
- once bitten, twice shy
- once in a blue moon
- (every) once in a while
- once or twice
- once too often
- once upon a time
■ conjunction
as soon as; when :
We didn't know how we would cope once the money had gone.
The water is fine once you're in!
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WORD ORIGIN
Middle English ones , genitive of one . The spelling change in the 16th cent. was in order to retain the unvoiced sound of the final consonant.