The Collaborative International Dictionary of English v.0.48:

Moss \Moss\ (m[o^]s; 115), n. [OE. mos; akin to AS. me['o]s, D.
   mos, G. moos, OHG. mos, mios, Icel. mosi, Dan. mos, Sw.
   mossa, Russ. mokh', L. muscus. Cf. Muscoid.]
   1. (Bot.) A cryptogamous plant of a cellular structure, with
      distinct stem and simple leaves. The fruit is a small
      capsule usually opening by an apical lid, and so
      discharging the spores. There are many species,
      collectively termed Musci, growing on the earth, on rocks,
      and trunks of trees, etc., and a few in running water.
      [1913 Webster]

   Note: The term moss is also popularly applied to many other
         small cryptogamic plants, particularly lichens, species
         of which are called tree moss, rock moss, coral moss,
         etc. Fir moss and club moss are of the genus
         Lycopodium. See Club moss, under Club, and
         Lycopodium.
         [1913 Webster]

   2. A bog; a morass; a place containing peat; as, the mosses
      of the Scottish border.
      [1913 Webster]

   Note: Moss is used with participles in the composition of
         words which need no special explanation; as,
         moss-capped, moss-clad, moss-covered, moss-grown, etc.
         [1913 Webster]

   Black moss. See under Black, and Tillandsia.

   Bog moss. See Sphagnum.

   Feather moss, any moss branched in a feathery manner, esp.
      several species of the genus Hypnum.

   Florida moss, Long moss, or Spanish moss. See
      Tillandsia.

   Iceland moss, a lichen. See Iceland Moss.

   Irish moss, a seaweed. See Carrageen.

   Moss agate (Min.), a variety of agate, containing brown,
      black, or green mosslike or dendritic markings, due in
      part to oxide of manganese. Called also Mocha stone.

   Moss animal (Zool.), a bryozoan.

   Moss berry (Bot.), the small cranberry (Vaccinium
      Oxycoccus).

   Moss campion (Bot.), a kind of mosslike catchfly (Silene
      acaulis), with mostly purplish flowers, found on the
      highest mountains of Europe and America, and within the
      Arctic circle.

   Moss land, land produced accumulation of aquatic plants,
      forming peat bogs of more or less consistency, as the
      water is grained off or retained in its pores.

   Moss pink (Bot.), a plant of the genus Phlox (Phlox
      subulata), growing in patches on dry rocky hills in the
      Middle United States, and often cultivated for its
      handsome flowers. --Gray.

   Moss rose (Bot.), a variety of rose having a mosslike
      growth on the stalk and calyx. It is said to be derived
      from the Provence rose.

   Moss rush (Bot.), a rush of the genus Juncus (Juncus
      squarrosus).

   Scale moss. See Hepatica.
      [1913 Webster]

WordNet (r) 3.0 (2006):

moss agate
    n 1: an agate resembling moss with brown, black, or green
         markings