Where does the word smarm come from?

Factual Questions
1

Merriam-Webster and Dictionary.com both say that the adjective “smarmy” is derived from a verb “smarm”, which means either “to gush, slobber” (M-W) or “to smear” (Dictionary.com). However, neither site actually has that definition of “smarm”; they only have a noun definition, and they claim it’s a back formation from “smarmy”.

What’s the straight dope on the verb form of “smarm”? When was it used, and in what language?

2

From my *Chambers–Dictionary of Etymology. *

"adj. Informal. offesively flattering or ingratiating. 1924, formed in English from earlier smarm to behave in a flattering way(1920), variant of smalm (1890) and smawm(1846) to smear, bedaub, of unknown origin; "