moss: [OE] The prehistoric Germanic ancestor of moss was *musam. This had two distinct meanings: ‘swamp’ and ‘moss’. It is not altogether clear which was primary, but it seems more probable than not that ‘moss’ (a plant which frequents damp places) was derived from ‘swamp’. The only meaning recorded for its Old English descendant mos was ‘swamp’ (which survives in place-names), but no doubt ‘moss’ (not evidenced before the 14th century) was current too.
Words from the same ultimate source to have found their way into English include mire [14] (borrowed from Old Norse mýrr ‘swamp’), mousse [19] (borrowed from French, which got it from Middle Low German mos ‘moss’), and litmus [16] (whose Old Norse source litmosi meant literally ‘dye-moss’ – litmus is a dye extracted from lichens). => litmus, mire, mousse[moss etymology, moss origin, 英语词源]