The Collaborative International Dictionary of English v.0.48:

Auntie \Aunt"ie\, Aunty \Aunt"y\, n.
   A familiar name for an aunt. In the southern United States a
   familiar term applied to aged negro women.
   [1913 Webster]

WordNet (r) 3.0 (2006):

auntie
    n 1: the sister of your father or mother; the wife of your uncle
         [syn: aunt, auntie, aunty] [ant: uncle]