The Collaborative International Dictionary of English v.0.48:

Thoroughly \Thor"ough*ly\, adv.
   In a thorough manner; fully; entirely; completely.
   [1913 Webster]

WordNet (r) 3.0 (2006):

thoroughly
    adv 1: in an exhaustive manner; "we searched the files
           thoroughly" [syn: thoroughly, exhaustively]
    2: completely and absolutely (`good' is sometimes used
       informally for `thoroughly'); "he was soundly defeated"; "we
       beat him good" [syn: thoroughly, soundly, good]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "thoroughly":
   absolutely, altogether, assiduously, backwards and forwards,
   carefully, cautiously, circumspectly, completely, comprehensively,
   conscientiously, considerately, definitely, diligently, dingdong,
   downright, earnestly, entirely, exceedingly, exceptionally,
   exhaustively, extensively, extremely, faultlessly, flawlessly,
   fully, globally, heedfully, highly, hugely, hundred per cent,
   ideally, immaculately, impeccably, in and out, in full,
   in full measure, inclusively, industriously, infallibly,
   inside out, integrally, intensely, intensively, item by item,
   just right, largely, lovingly, methodically, meticulously,
   mindfully, notably, one and all, outright, painstakingly,
   perfectly, plumb, positively, purely, quite, rattling, regardfully,
   remarkably, roundly, scrupulously, sedulously, solicitously,
   spotlessly, strikingly, tenderly, thoroughgoingly, thoughtfully,
   throughout, to the hilt, totally, tout a fait, unconditionally,
   unremittingly, unreservedly, up and down, utterly, wholly,
   with care, with great care