Green’s Dictionary of Slang

a cat’s whiskers.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1849		Paul Pry 29 Jan. 4/3: ‘Pussey,’ [...] quietly mewed, pawed his smellers, and wagged his tail.