From Longman Dictionary of Contemporary Englishhaystackhay‧stack /ˈheɪstæk/ (also hayrick) noun [countable] TAa large, firmly built pile of hay → like looking for a needle in a haystack at needle1(7)
Examples from the Corpus
haystack• It would be like looking for a needle in a haystack.• And getting a grin out of Dooley Barlowe was like looking for a needle in a haystack.• Do I hear a murmur about needles and haystacks?• My sister is looking for a recipe for haystacks, which are a vanilla-flavored candy with coconut.• Tall bamboos appeared beside the highway again, and a settlement with low wooden shops, and thatched huts like haystacks.• They were launched atop a pillow of water covering a rock, slid off, then rode out a landscape of haystacks.• Tempers flared: Three hundred officers took part in operation haystack. 