The Collaborative International Dictionary of English v.0.48:

Prima donna \Pri"ma don"na\; pl. E. Prima donnas, It. Prime
   Donne . [It., fr. primo, prima, the first + donna lady,
   mistress. See {Prime, a., and Donna.]
   The first or chief female singer in an opera.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prima donna
    n 1: a vain and temperamental person
    2: a distinguished female operatic singer; a female operatic
       star [syn: prima donna, diva]