(chiefly Britain, dated in US, idiomatic) Insane, crazy.

(idiomatic) A problem that is challenging to solve. / (idiomatic, by extension) A situation, person, group, etc. which is difficult to deal with.

A cylindrical push-and-twist connector for thin coaxial cable.

Time to gather nuts before they are taken by other animals or buried in snow. / (idiomatic) Time to exert maximum effort, for example, due to an approaching deadline or a looming competitive situation.

(intransitive, slang) To become stridently angry, especially from worry.

brown butter

plural of barrel nut connector

Used other than figuratively or idiomatically: see hard, nut, crack. / (idiomatic) A problem that is challenging to solve.

Alternative form of hard nut to crack

Alternative form of tough nut to crack