Green’s Dictionary of Slang

plush n.

[SE plush, a type of cloth, softer than velvet, used for expensive garments, seat covers etc.]

1. [19C] female pubic hair [note Ital. peluccio, peluzzo, a little hair, soft down, fine hair].

2. [mid-19C-1910s] (orig. RN) profit, money .

SE in slang uses

In phrases

on (the) plush (adv.)

[1920s–40s] in luxury.

sit in the plush (v.)

[1910s-40s] to live in luxury.