The Collaborative International Dictionary of English v.0.48:

Lukewarm \Luke"warm`\ (l[=u]k"w[add]rm`), a. [See Luke.]
   1. Moderately warm; neither cold nor hot; tepid.
      [1913 Webster]

   2. Not ardent; not zealous; cool; indifferent. " Lukewarm
      blood." --Spenser. " Lukewarm patriots." --Addison.
      [1913 Webster]

            An obedience so lukewarm and languishing that it
            merits not the name of passion.       --Dryden.
      -- Luke"warm`ly, adv. -- Luke"warm`ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

lukewarm
    adj 1: moderately warm; "he hates lukewarm coffee"; "tepid bath
           water" [syn: lukewarm, tepid]
    2: feeling or showing little interest or enthusiasm; "a
       halfhearted effort"; "gave only lukewarm support to the
       candidate" [syn: halfhearted, half-hearted, tepid,
       lukewarm]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "lukewarm":
   Laodicean, aestival, apathetic, blood-hot, blood-warm, calid,
   chill, chilly, cold, cool, equatorial, fervorless, genial,
   half-baked, halfhearted, hesitant, indecisive, indevotional,
   indevout, indifferent, indifferentist, insouciant, irresolute,
   irresolved, lackadaisical, luke, mild, neuter, neutral, nonchalant,
   nonobservant, nonreligious, perfunctory, phlegmatic,
   room temperature, room-temperature, subtropical, summery, sunny,
   sunshiny, temperate, tepid, thermal, thermic, toasty, tropical,
   uncertain, uncommitted, undecided, undevout, undutiful,
   unenthusiastic, unfrozen, unmoved, unreligious, unresolved,
   unresponsive, warm, warm as toast, warmish, wishy-washy,
   zealless