muddy (adj.)

late 13c., in place names, "abounding in or covered with mud," from mud + -y (2). Meaning "not clear or pure in color" is from 1580s; extended to sounds by 1960s. Big Muddy as a nickname for the Missouri or Mississippi river is attested by 1825. Related: Muddily; muddiness.

"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.