The Collaborative International Dictionary of English v.0.48:

Appreciable \Ap*pre"ci*a*ble\, a. [Cf. F. appr['e]ciable.]
   Capable of being appreciated or estimated; large enough to be
   estimated; perceptible; as, an appreciable quantity. --
   Ap*pre"ci*a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

appreciably
    adv 1: to a noticeable degree; "they weather was appreciably
           colder"

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "appreciably":
   after a fashion, at any rate, at best, at least, at most,
   at the least, at the most, at the outside, at worst, comparatively,
   detectably, fairly, in a manner, in a way, in part,
   in some measure, incompletely, leastwise, measurably, merely,
   mildly, moderately, modestly, not comprehensively,
   not exhaustively, noticeably, only, part, partially, partly,
   perceptibly, pro tanto, purely, relatively, simply, so far,
   somewhat, thus far, to a degree, to some degree, tolerably,
   visibly