Green’s Dictionary of Slang

nyam v.

also niam, nom
[var. on yam v.]

1. [early 18C+] (orig. W.I.) to eat.

2. [1950s] (orig. W.I.) to taste.

3. [1970s+] (UK black) in fig. use, to attack, to arrest.

In compounds

nyam dog (n.) [SE dog; the Chinese predilection for cooking dog]

[1940s] (W.I.) a Chinese person.