FAW, FUM. Nonsensical words, supposed in childish story-books to be spoken by giants. I am not to be frighted by fee, faw, fum; I am not to be scared by nonsense.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Feather-bed Lane * FeederNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes