(~s)
1.
A ~ is a metal tool whose end fits round a nut so that you can turn it to loosen or tighten it. (mainly BRIT; in AM, usually use wrench , monkey wrench )
N-COUNT
2.
If someone throws a ~ in the works, they prevent something happening smoothly in the way that it was planned, by causing a problem or difficulty. (BRIT; in AM, use throw a wrench , throw a monkey wrench )
A bad result is sure to throw a ~ in the works.
PHRASE: V inflects