Green’s Dictionary of Slang

nosh v.

also knosh, nash
[Yid. nosh, to snack and Ger. naschen, to nibble, to eat surreptitiously; mainly US but note The Nosh Bar, a long lived delicatessen/cafe in Great Windmill Street, Soho, London]

1. [late 19C+] to eat, esp. to snack, to eat between meals; occas. to drink.

2. [1970s+] to practise oral sex [pun on sense 1].