The Collaborative International Dictionary of English v.0.48:

Whinny \Whin"ny\, v. i. [imp. & p. p. Whinnied; p. pr. & vb.
   n. Whinnying.] [From Whine]
   To utter the ordinary call or cry of a horse; to neigh.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Whinny \Whin"ny\, n.; pl. Whinnies.
   The ordinary cry or call of a horse; a neigh. "The stately
   horse . . . stooped with a low whinny." --Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Whinny \Whin"ny\, a.
   Abounding in whin, gorse, or furze.
   [1913 Webster]

         A fine, large, whinny, . . . unimproved common.
                                                  --Sterne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

whinny
    n 1: the characteristic sounds made by a horse [syn: neigh,
         nicker, whicker, whinny]
    v 1: make a characteristic sound, of a horse [syn: neigh,
         nicker, whicker, whinny]