haystack
n. countable B2 Upper Intermediate US //ˈheɪˌstæk// UK //hˈeɪstæk// haystack
n. a large pile of dried grass or straw. It is also used to describe a situation where it is very hard to find what you are looking for.
n. a large, round pile of dried grass or straw. In a figurative sense, it refers to a large, disorganized collection of data or objects from which a specific item is difficult to locate.
The farmer stacked the hay into a large haystack.
Finding a specific document in that old filing cabinet is like looking for a needle in a haystack.
The software engineer optimized the search algorithm to ensure that even within a massive haystack of unstructured data, the relevant results would be surfaced in milliseconds.
From Middle English haystak, haystake, hey stak, equivalent to hay + stack.