Source : Webster's Revised Unabridged Dictionary (1913)

Ninny \Nin"ny\, n.; pl. {Ninnies}. [Cf. It. ninno, ninna, a
   baby, Sp. ni[~n]o, ni[~n]a, child, infant, It. ninna, ninna
   nanna, lullably, prob. fr. ni, na, as used in singing a child
   to sleep.]
   A fool; a simpleton. --Shak.

Source : WordNet®

ninny
     n : a stupid foolish person [syn: {nincompoop}, {poop}]