adverb (r)

• without delay or hesitation; with no time intervening(adv.all)

  Synonym:
  at once, directly, forthwith, immediately, like a shot, now, right away, straight off, straightaway
  

  source: wordnet30
• without any delay(adv.all)

  Synonym:
  in a flash, instantaneously, outright
  

  source: wordnet30
• Without the least delay or interval; at once; immediately.(adverb)

  source: webster1913