"ponder," 1873, perhaps from a figurative use of Middle English mullyn "grind to powder, pulverize," from molle "dust, ashes, rubbish" (c.1300), probably from Middle Dutch mul "grit, loose earth," related to mill (n.1). But Webster's (1879) defined it as "to work steadily without accomplishing much," which may connect it to earlier identical word in athletics sense of "to botch, muff" (1862). Related: Mulled; mulling.
"sweeten, spice and heat a drink," c.1600, of unknown origin, perhaps from Dutch mol, a kind of white, sweet beer, or from Flemish molle a kind of beer, and related to words for "to soften." Related: Mulled; mulling.
"promontory" (in Scottish place names), late 14c., perhaps from Old Norse muli "a jutting crag, projecting ridge (between two valleys)," which probably is identical with muli "snout, muzzle." The Norse word is related to Old Frisian mula, Middle Dutch mule, muul, Old High German mula, German Maul "muzzle, mouth." Alternative etymology traces it to Gaelic maol "brow of a hill or rock," also "bald," from Old Celtic *mailo-s (cf. Irish maol, Old Irish máel, máil, Welsh moel).