WordNet (r) 3.0 (2006):

straightaway
    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]
    adj 1: performed with little or no delay; "an immediate reply to
           my letter"; "a prompt reply"; "was quick to respond"; "a
           straightaway denial" [syn: immediate, prompt,
           quick, straightaway]
    n 1: a straight segment of a roadway or racecourse [syn:
         straightaway, straight]

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "straightaway":
   PDQ, air line, all at once, all together, apace, at a blow,
   at a stroke, at once, at one blow, at one jump, at one stroke,
   at one swoop, at one time, away, axis, beeline, chord, decisively,
   diagonal, diameter, direct, direct line, directly, directrix, edge,
   expeditiously, first, forthwith, great-circle course, immediate,
   immediately, in a hurry, in no time, instanter, instantly,
   irreversible, normal, now, on the instant, on the spot, one-way,
   per saltum, perpendicular, pretty damned quick, promptly, pronto,
   quickly, radius, radius vector, right away, right line, right now,
   right off, secant, segment, shortcut, side, simultaneously,
   smartly, speedily, straight, straight course, straight line,
   straight stretch, straightforward, straightway, streamline, subito,
   summarily, swiftly, tangent, then and there, this minute,
   this very minute, transversal, unbroken, undeviating,
   unidirectional, uninterrupted, uno saltu, unswerving, vector,
   with all speed, without delay, without further delay