This is from Collins English dictionary;
knackered (?næk?d Pronunciation for knackered )
Definitions;
adjective
(British, slang)
exhausted; tired out; worn out; no longer working, esp after long or hard use
Synonyms
View thesaurus entry;
= exhausted, worn out, tired out, drained, beat, done in, all in, buggered, debilitated, prostrated, enervated, ready to drop, dog-tired, zonked, dead tired, dead beat
= broken, not working, out of order, not functioning, done in, ruined, buggered, worn out, on the blink, on its last legs
knacker (?næk? Pronunciation for knacker ) (British)
Definitions;
noun
a person who buys up old horses for slaughter
a person who buys up old buildings and breaks them up for scrap
(usually plural) (slang) another word for testicle
(Irish, slang) a despicable person
verb
(transitive; usually passive) (slang) to exhaust; tire
Word Origin;
C16: probably from nacker saddler, probably of Scandinavian origin; compare Old Norse hnakkur saddle