A large stack of hay, especially as left in a field to dry. Also called hayrick. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "haystack" in a sentence
"NSA thinks the way you find a needle in a haystack is to add more hay."
"Case researchers discover methods to find 'needles in haystack' in data"
"The competition is administered by HASTAC "haystack"---Humanities, Arts, Science, and Technology Advanced Collaboratory, an innovative "Web 2.0" virtual institution of more than eighty institutes, centers, and community organizations anchored at the University of California Humanities Research Institute and the John Hope Franklin Center at Duke University."