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. frequency One and only one time.
2. adv. temporal location Formerly; during some period in the past.
3. adv. mathematics multiplied by one: indicating that a number is multiplied by one
4. conj. As soon as; when; after.

GNU Webster's 1913

1. n. (Zoöl.) 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