The Collaborative International Dictionary of English v.0.48:

Immediately \Im*me"di*ate*ly\, adv.
   1. In an immediate manner; without intervention of any other
      person or thing; proximately; directly; -- opposed to
      mediately; as, immediately contiguous.
      [1913 Webster]

            God's acceptance of it either immediately by
            himself, or mediately by the hands of the bishop.
                                                  --South.
      [1913 Webster]

   2. Without interval of time; without delay; promptly;
      instantly; at once.
      [1913 Webster]

            And Jesus . . . touched him, saying, I will; be thou
            clean. And immediately his leprosy was cleansed.
                                                  --Matt. viii.
                                                  3.
      [1913 Webster]

   3. As soon as. Cf. Directly, 8, Note.

   Syn: Directly; instantly; quickly; forthwith; straightway;
        presently. See Directly.
        [1913 Webster]

WordNet (r) 3.0 (2006):

immediately
    adv 1: without delay or hesitation; with no time intervening;
           "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, at once,
           forthwith, like a shot]
    2: near or close by; "he passed immediately behind her"
    3: bearing an immediate relation; "this immediately concerns
       your future"

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "immediately":
   PDQ, amain, anon, apace, at once, away, by forced marches, closely,
   contiguously, cursorily, decisively, directly, expeditiously,
   feverishly, forthwith, furiously, hand over fist, hastily,
   helter-skelter, hotfoot, hurriedly, hurry-scurry, in a jiffy,
   in a second, in a wink, in no time, in passing, instantaneously,
   instanter, instantly, intimately, just now, just then,
   momentaneously, momentarily, momently, now, on the dot,
   on the instant, on the nail, on the run, on the spot, pell-mell,
   pretty damned quick, promptly, pronto, quickly, right away,
   right now, right off, shortly, slapdash, smartly, soon, speedily,
   straightaway, straightway, subito, summarily, superficially,
   swiftly, this instant, tout de suite, when, with a rush,
   with all haste, with all speed, with dispatch, with haste,
   without delay, without further delay, without hesitation