knackered

Concise Oxford English Dictionary © 2008 Oxford University Press:
knacker /ˈnakə(r)/ Brit.

▶noun

• 1 a person who disposes of dead or unwanted animals.

• 2 (knackers) vulgar slang testicles.

▶verb (often as adj. knackered) informal exhaust; wear out.

■ damage (something) severely.

– origin C16 (orig. denoting a harness maker): possibly from obs. knack ‘trinket’; sense 2 of the noun may be from dial. knacker ‘castanet’.