–adverb
1.at one time in the past; formerly: I was a farmer once; a once powerful nation.
2.a single time: We ate there just once. We go to a movie once a week.
3.even a single time; at any time; ever: If the facts once become known, it will be just too bad.
4.by a single step, degree, or grade: a cousin once removed.
–adjective
5.former; having at one time been: the once and future king.
–conjunction
6.if or when at any time; if ever.
7.whenever; as soon as: Once you're finished, you can leave.
–noun
8.a single occasion; one time only: Once is enough.