Third person singular of cack, or plural noun; British slang for trousers or underwear.
As a verb form, third person singular of cack. As a noun, possibly from cack or independently derived slang for clothing, particularly underwear in British English.
'Cacks' meaning trousers is pure British working-class slang—it's a word that would be completely incomprehensible to American English speakers but perfectly clear to Londoners.
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