The Collaborative International Dictionary of English v.0.48:

Tepidity \Te*pid"i*ty\, n. [Cf. F. t['e]pidit['e].]
   The quality or state of being tepid; moderate warmth;
   lukewarmness; tepidness. --Jer. Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tepidity
    n 1: a warmness resembling the temperature of the skin [syn:
         lukewarmness, tepidity, tepidness]