once

American Heritage® Dictionary of the English Language, Fourth Edition

1. adv. One time only: once a day.
2. adv. At one time in the past; formerly.
3. adv. At any time; ever: Once known, his face is never forgotten.
4. adv. By one degree of relationship: my first cousin once removed.
5. n. A single occurrence; one time: Once will have to do. You can go just this once.
6. conj. As soon as; if ever; when: Once he goes, we can clean up.
7. adj. Having been formerly; former: the once capital of the nation.
8. idiom. at once All at one time; simultaneously: Everything happened at once. The view of the skyline is at once awesome, grand, and disappointing.
9. idiom. at once Immediately; instantly: Leave the room at once.

Century Dictionary and Cyclopedia

1. One time.
2. One and the same time: usually with at: as, they all cried out at once. See phrases below.
3. At one time in the past; formerly.
4. At some future time; some time or other.
5. At any time; in any contingency; on any occasion; under any circumstances; ever.
6. Without delay; immediately: often merely expletive: as, John, come here once.
7. Once for all.
8. Immediately; forthwith; without delay.
9. When at any time; whenever; as soon as.
10. n. An obsolete form of ounce.

Wiktionary

1. adv. one and only one time
2. adv. formerly
3. conj. as soon as

GNU Webster's 1913

1. n. The ounce.
2. adv. For one time; by limitation to the number one; not twice nor any number of times more than one.
3. adv. At some one period of time; -- used indefinitely.
4. adv. At any one time; -- often nearly equivalent to ever, if ever, or whenever.

WordNet 3.0

1. adv. as soon as
2. adv. at a previous time
3. adv. on one occasion