The Collaborative International Dictionary of English v.0.48:

Somniloquy \Som*nil"o*quy\, n.
   A talking in sleep; the talking of one in a state of
   somnipathy. [R.] --Coleridge.
   [1913 Webster]

WordNet (r) 3.0 (2006):

somniloquy
    n 1: uttering speech while asleep [syn: sleep talking,
         somniloquy, somniloquism]