The Collaborative International Dictionary of English v.0.48:

Haystack \Hay"stack`\ (h[=a]"st[a^]k`), n.
   A stack or conical pile of hay in the open air.
   [1913 Webster]

WordNet (r) 3.0 (2006):

haystack
    n 1: a stack of hay [syn: haystack, hayrick, rick]