1852, from verbal phrase, stick (v.) on notion of "one who sticks in the mud," hence "one who is content to remain in an abject condition." The phrase appears in 1730, in city of London court records, as the alias of an accused named John Baker, who with two other men received a death sentence at the Old Bailey in December 1733 for "breaking open the House of Mr. Thomas Rayner, a Silversmith, and stealing thence Plate to a great Value."
"mud," 1824, from Irish and Gaelic clabar "mud." Also often short for bonnyclabber. As a verb, "become thick" (of milk, etc.), by 1880.
"mud, mire, ooze," 1640s, a word of uncertain origin, possibly a variant of Middle English slutch "mud, mire," or of slush (n.). Related: Sludgy.
"to make muddy, bury or cover with mud," c. 1600, from muddy (adj.). Related: Muddied; muddying. The earlier verb was simply mud (1590s); muddify is attested from 1789.