The Collaborative International Dictionary of English v.0.48:

Clue \Clue\ (kl[=u]), n. [See Clew, n.]
   A ball of thread; a thread or other means of guidance. Same
   as Clew.
   [1913 Webster]

         You have wound a goodly clue.            --Shak.
   [1913 Webster]

         This clue once found unravels all the rest. --Pope.
   [1913 Webster]

         Serve as clues to guide us into further knowledge.
                                                  --Locke.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Clew \Clew\ (kl[=u]), Clue \Clue\, n. [OE. clewe, clowe, clue,
   AS. cleowen, cliwen, clywe ball of thread; akin to D. kluwen,
   OHG. chliwa, chliuwa, G. dim. kleuel, kn[aum]uel, and perch.
   to L. gluma hull, husk, Skr. glaus sort of ball or tumor.
   Perch. akin to E. claw. [root]26. Cf. Knawel.]
   1. A ball of thread, yarn, or cord; also, The thread itself.
      [1913 Webster]

            Untwisting his deceitful clew.        --Spenser.
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   2. That which guides or directs one in anything of a doubtful
      or intricate nature; that which gives a hint in the
      solution of a mystery.
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            The clew, without which it was perilous to enter the
            vast and intricate maze of countinental politics,
            was in his hands.                     --Macaulay.
      [1913 Webster]

   3. (Naut.)
      (a.) A lower corner of a square sail, or the after corner
           of a fore-and-aft sail.
      (b.) A loop and thimbles at the corner of a sail.
      (c.) A combination of lines or nettles by which a hammock
           is suspended.
           [1913 Webster]

   Clew garnet (Naut.), one of the ropes by which the clews of
      the courses of square-rigged vessels are drawn up to the
      lower yards.

   Clew line (Naut.), a rope by which a clew of one of the
      smaller square sails, as topsail, topgallant sail, or
      royal, is run up to its yard.

   Clew-line block (Naut.), The block through which a clew
      line reeves. See Illust. of Block.
      [1913 Webster]

WordNet (r) 3.0 (2006):

clue
    n 1: a slight indication [syn: hint, clue]
    2: evidence that helps to solve a problem [syn: clue, clew,
       cue]
    v 1: roll into a ball [syn: clue, clew]

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "clue":
   acquaint, advice, advise, alerting, answer, apprise,
   basis for belief, body of evidence, broad hint, catchword, caution,
   chain of evidence, cue, cue word, data, datum, documentation,
   evidence, exhibit, fact, facts, fill in, gentle hint, gesture,
   glimmer, glimmering, grounds, grounds for belief, hint, hot lead,
   implication, imply, index, indicate, indication, indicator, inform,
   information, inkling, innuendo, insinuation, intimate, intimation,
   item of evidence, key, key word, kick, lead, look, manifestation,
   mark, material grounds, monition, muniments, mute witness, nod,
   notify, notion, nudge, office, passing word, piece of evidence,
   pointer, post, premises, prompt, proof, reason to believe,
   relevant fact, scent, sign, signal, spoor, steer, suggest,
   suggestion, suspicion, symptom, tell, telltale, tip, tip-off,
   token, trace, track, vestige, warn, warning, whiff, whisper, wind,
   wink