Definition

1. Adverb:

   • At one time in the past; formerly: Refers to a situation that was true at an unspecified time in the past but is no longer true.
   • One single time; on one occasion: Indicates that an action happened or happens one time only.
   • At any time; ever: Used in negative or conditional contexts to mean 'at any time' or 'ever'.

2. Conjunction:

   • As soon as; when: Used to indicate that something happens immediately after or at the moment something else happens.

Usage Examples

• Adverb (formerly):
  • This city was once a small village.
  • I once believed in magic.
• Adverb (one time):
  • I have been to Paris only once.
  • Call me once you arrive.
• Adverb (ever - in negative contexts):
  • If you once start complaining, you'll never stop.
• Conjunction (as soon as):
  • Once you understand the rules, the game becomes easy.
  • Once the rain stops, we can go outside.

Advanced Usage

• "all at once": suddenly; all together at the same time.
  • All at once, the lights went out.
  • The audience stood up all at once.
• "at once": immediately; simultaneously.
  • You must leave at once.
  • She can do two things at once.
• "for once": on this (or that) single occasion, especially as an exception.
  • For once, he arrived on time.
• "once and for all": finally and conclusively.
  • Let's settle this argument once and for all.

Variants and Related Words

• Once-over (noun): a quick look or inspection.
  • He gave the document a quick once-over.
• Oncer (noun, informal, chiefly British): a person who does something only once, or a thing that occurs only once.

Synonyms

• Adverb (formerly): formerly, previously, at one time, in the past.
• Adverb (one time): one time, a single time.
• Conjunction: as soon as, when, after.

Related Phrases and Idioms

• Once in a blue moon: very rarely.
  • He visits us once in a blue moon.
• Once upon a time: used at the beginning of fairy tales to mean 'a long time ago in the past'.
  • Once upon a time, there was a beautiful princess.
• Once bitten, twice shy: after an unpleasant experience, one is cautious in similar situations.
• Once in a while: occasionally; sometimes but not often.
  • We go out for dinner once in a while.

Adverb

1. at a previous time;
   • at one time he loved her
   • her erstwhile writing
   • she was a dancer once
2. as soon as
   • once we are home, we can rest
3. on one occasion
   • once I ran into her