From Middle English mos, from Old English mos (“bog, marsh, moss”), from Proto-Germanic *musą (“marsh, moss”), from Proto-Indo-European *mūs-, *meus- (“moss”). Cognate with Old High German mos (German Moos, “moss”), Icelandic mosi, Danish mos, Swedish mossa, Latin muscus (“moss”).
moss (countable and uncountable; plural mosses)
- (now chiefly UK regional) A bog; a swamp.
- Any of various small green plants growing on the ground or on the surfaces of trees, stones etc.; now specifically, a plant of the division Bryophyta (formerly Musci).
- (countable) A type or species of such plant.
Usage notes 
- The plural form mosses is used when more than one kind of moss is meant. The singular moss is used referring to a collection of moss plants of the same kind.
Derived terms 
Terms derived from the noun moss
plants of the division Bryophyta
a clump or patch of such plants
moss (third-person singular simple present mosses, present participle mossing, simple past and past participle mossed)
- (intransitive) To become covered with moss.
- An oak whose boughs were mossed with age.
- (transitive) To cover (something) with moss.
to become covered with moss
cover (something) with moss
See also