"strawy dung, loose earth, leaves, etc., spread on the ground to protect shoots or newly planted shrubs," 1650s, probably a noun use of Middle English molsh (adj.) "soft, moist" (mid-15c.), from Old English melsc, milisc "mellow, sweet," from Proto-Germanic *mil-sk- (source also of Dutch mals "soft, ripe," Old High German molawen "to become soft," German mollig "soft"), from PIE root *mel- (1) "soft."
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."