haystack

1. N-COUNT A haystack is a large, solid pile of hay, often covered with a straw roof to protect it, which is left in the field until it is needed. (露天)干草堆

2. PHRASE If you are trying to find something and say that it is like looking for a needle in a haystack, you mean that you are extremely unlikely to find it. 比喻如大海捞针般难找