Green’s Dictionary of Slang

lam n.2

[lam v.1 ]

(US) a punch or blow.

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[US]Wkly Rake (NY) 3 Sept. n.p.: Keep up your courage, give harder your ‘lam’ .
[US]K. McGaffey Sorrows of a Show Girl Ch. xii: I thought she was going to give the poor kid a lam on the lamp.
[US]H. Roth Call It Sleep (1977) 289: Wanna ged a lam onnuh eye?

In phrases

have a lam on (v.) [? the temper occasions the blows]

to be in a bad temper.

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[Scot]I. Welsh Trainspotting 330: The cunt’s goat a lam on because ah’ve been pokin his wee slut ay a daughter.