Earlier in English as achate (early 13c.), directly from Latin. The Elizabethan sense of "a diminutive person" is from the small figures cut in agates for seals, etc., and the notion of smallness is preserved in typographer's agate (1838), the U.S. name of the 5.5-point font called in Great Britain ruby. Meaning "toy marble made of glass resembling agate" is from 1843 (colloquially called an aggie). Related: Agatine.
type of toy marble, by 1905, American English, colloquial shortening of agate (q.v.).
Excited groups gather about rude circles scratched in the mud, and there is talk of "pureys," and "reals," and "aggies," and "commies," and "fen dubs!" There is a rich click about the bulging pockets of the boys, and every so often in school time something drops on the floor and rolls noisily across the room. When Miss Daniels asks: "Who did that?" the boys all look so astonished. Who did what pray tell? [McClure's magazine, May 1905]
In 19c. also used of other raised, carved work on a miniature scale. Transferred sense of "small character or part that stands out from other minor parts" in a play, etc., is from 1928, from earlier meaning "short literary sketch or portrait" (1851), a transferred sense from cameo silhouettes. A cameotype (1864) was a small, vignette daguerreotype mounted in a jeweled setting.
the meanings "mass of small, cryptogamous, herbaceous plants growing together" and "bog, peat-bog" are the same word: Old English meos "moss plant" and mos "bog;" both are from Proto-Germanic *musan (source also of Old High German mios, Danish mos, German Moos), also in part from Old Norse mosi "moss, bog," and Medieval Latin mossa "moss," from the same Germanic source.
These are from PIE *meus- "damp," with derivatives referring to swamps and swamp vegetation (source also of Latin muscus "moss," Lithuanian mūsai "mold, mildew," Old Church Slavonic muchu "moss"). The Germanic languages have the word in both senses, which is natural because moss is the characteristic plant of boggy places. It is impossible to say which sense is original. The proverb that a rolling stone gathers no moss is suggested from 14c.:
Selden Moseþ þe Marbelston þat men ofte treden. ["Piers Plowman," 1362]
Moss-agate "agate stone with moss-like dendrite forms (caused by metallic oxides)" is from 1790. Scott (1805) revived 17c. moss-trooper "freebooter infesting Scottish border marshes" (compare bog-trotter).