'once' definitions:

Definition of 'once'

From: WordNet
adverb
On one occasion; "once I ran into her" [syn: once, one time, in one case]
adverb
As soon as; "once we are home, we can rest"
adverb
At a previous time; "at one time he loved her"; "her erstwhile writing"; "she was a dancer once"; [syn: once, formerly, at one time, erstwhile, erst]

Synonyms of 'once'

From: Moby Thesaurus