Muck
Middle English muk, probably of Scandinavian origin: compare with Old Norse myki ‘dung’, from a Germanic base meaning ‘soft’, shared by meek.
wiktionary
From Middle English mok, muk, from Old Norse myki, mykr(“dung”) or less likely Old English *moc (in hlōsmoc(“pigsty dung”)) (compare Icelandic mykja and Danish møg ("dung")), from Proto-Germanic *mukī(“dung; manure”), from Proto-Indo-European *(s)mewg-, *mewk-(“slick, slippery”) (compare Welsh mign(“swamp”), Latin mūcus(“snot”), mucere(“to be moldy or musty”), Latvian mukls(“swampy”), Albanian myk(“mould”), Ancient Greek mýxa 'mucus, lamp wick', mýkes 'fungus'), from *(s)mewg, mewk 'to slip'. More at meek.
etymonline
muck (n.)
mid-13c., muk, "animal or human excrement; cow dung and vegetable matter spread as manure," from a Scandinavian source such as Old Norse myki, mykr "cow dung," Danish møg; from Proto-Germanic *muk-, *meuk- "soft," which is perhaps related to Old English meox "dung, filth" (see mash (n.)). Meaning "unclean matter generally" is from c. 1300; that of "wet, slimy mess" is by 1766. Muck-sweat "profuse sweat" is attested from 1690s.
muck (v.)
late 14c., mukken, "to dig in the ground," also "to remove manure;" c. 1400, "to spread manure, cover with muck," from muck (n.) or Old Norse moka (n.). Mucker "one who removes muck from stables" is attested by early 13c. as a surname. Meaning "to make dirty" is from 1832; in the figurative sense, "to make a mess of," it is from 1886; to muck about "mess around" is from 1856. To muck (something) up is by 1896 as "to dirty, soil;" 1922 as "make a mess of." Related: Mucked; mucking.
