Time I Wʌns Met Change Adverb Cleans Car

• i've only been there once.
• he cleans his car once a week.
• she only sees her parents once every six months.
• for optimum effect, these drops are used once daily.

once

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.
• For optimum effect, these drops are used once daily.
• I had met Lou once before.
• Last year the region received rain only once.
• He only did it the once.
• Rome is a city you should visit at least once in your life.
• They meet once a week at a Paris café.
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.
• She remembers once travelling with her father to Kilkenny.
• I famously once said that I was a fighter and not a quitter.
• He once told an interviewer that his biggest regret was missing his father's funeral.
• It was once thought to be the best hotel in Europe.
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.
4. used with a preposition or another adverb to mean ‘as soon as somebody/something is/was’
• Once inside the gate, Sam hurried up the path.
5. suddenly
• All at once she lost her temper.
6. all together; at the same time
• SYNONYM simultaneously
  https://www.oxfordlearnersdictionaries.com/definition/english/simultaneously
• I can't do everything all at once—you'll have to be patient.
7. immediately; without delay
• Come here at once!
8. at the same time
• SYNONYM simultaneously
  https://www.oxfordlearnersdictionaries.com/definition/english/simultaneously
• Don't all speak at once!
• I can't do two things at once.
9. on this occasion (which is in contrast to what happens usually)
• Just for once he arrived on time.
• Can't you be nice to each other just this once?
10. said by an auctioneer to show that an item has been sold
11. one more time; another time
• Once again the train was late.
• Let me hear it just once more.
12. used to say that somebody cannot change
• Once an actor, always an actor.
13. after an unpleasant experience you are careful to avoid something similar
14. now and for the last time; finally or completely
• We need to settle this once and for all.
15. very rarely
16. occasionally
• Everybody makes a mistake once in a while.
17. a few times
• I don't know her well, I've only met her once or twice.
18. used to say that somebody has done something wrong or stupid again, and this time they will suffer because of it
• You've tried that trick once too often.
19. used, especially at the beginning of stories, to mean ‘a long time ago in the past’
• Once upon a time there was a beautiful princess.

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.