mud (n.)
mid-14c., cognate with and probably from Middle Low German mudde, Middle Dutch modde "thick mud," from Proto-Germanic *mud- from PIE *(s)meu-/*mu- [Buck], found in many words denoting "wet" or "dirty" (cognates: Greek mydos "damp, moisture," Old Irish muad "cloud," Polish muł "slime," Sanskrit mutra- "urine," Avestan muthra- "excrement, filth"); related to German Schmutz "dirt," which also is used for "mud" in roads, etc., to avoid dreck, which originally meant "excrement." Welsh mwd is from English. Replaced native fen.

Meaning "lowest or worst of anything" is from 1580s. As a word for "coffee," it is hobo slang from 1925; as a word for "opium" from 1922. To throw or hurl mud "make disgraceful accusations" is from 1762. To say (one's) name is mud and mean "(one) is discredited" is first recorded 1823, from mud in obsolete sense of "a stupid twaddling fellow" (1708). Mud in your eye as a toast recorded from 1912, American English. Mud puppy "salamander" is from 1889, American English; mud bath is from 1798; mud pie is from 1788.