Green’s Dictionary of Slang

plate v.1

[rhy. sl.; plate of ham = gam v.2 (1) or plate of meat = eat v. (4)]

to fellate; thus plating n.; plater n.

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implied in plating n.
[UK]G.F. Newman You Flash Bastard 197: ‘I’ll take a chance. Want you to plate me first anyway.’ That was something he doubted the woman was expecting. Few wanted to go down on their clients, but she didn’t resist.
[UK]P. Baker Fabulosa 296/2: plate to perform oral sex .

In phrases

plate the dish (v.)

(Polari) to perform anilingus.

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[UK]P. Baker Fabulosa 296/2: plate the dish anilingus .