Source : Webster's Revised Unabridged Dictionary (1913)

Roc \Roc\, n. [Ar. & Per. rokh or rukh. Cf. {Rook} a castle.]
   A monstrous bird of Arabian mythology. [Written also {rock},
   and {rukh}.] --Brande & C.

Source : WordNet®

roc
     n : mythical bird of prey having enormous size and strength