at once

Từ điển WordNet v3.1 - WordNet Dictionary

adverb

1. without delay or hesitation;
with no time intervening (Freq. 24)
- he answered immediately
- found an answer straightaway
- an official accused of dishonesty should be suspended forthwith
- Come here now!
• Syn:
immediately, instantly, straightaway, straight off, directly,
now, right away, forthwith, like a shot
• Derived from adjective:
immediate (for: immediately)
2. simultaneously (Freq. 9)
- he took three cookies at a time
• Syn:
at a time, at one time