The Collaborative International Dictionary of English v.0.48:

casaba \casaba\ n.
   a winter melon having a yellowish rind; -- called also
   casaba melon.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

casaba melon
    n 1: melon having yellowish rind and whitish flesh [syn:
         casaba, casaba melon]