c. 1400, "to wet, moisten," from Old French moillier "to wet, moisten" (12c., Modern French mouiller), from Vulgar Latin *molliare, from Latin mollis "soft," from PIE root *mel- (1) "soft." Sense of "drudge, labor, toil" (1540s) probably is via the notion of "to labor in dirt or mire." Related: Moiled; moiling.
It forms all or part of: amblyopia; bland; blandish; blenny; emollient; enamel; malacia; malaxation; malt; melt; mild; Mildred; milt; moil; mollify; Mollusca; mollusk; mulch; mullein; mutton; schmaltz; smelt (v.); smelt (n.).
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit mrdh "to neglect," also "to be moist;" Greek malakos "soft," malthon "weakling;" Latin mollire "soften," mollis "soft;" Old Irish meldach "tender."