c. 1400, compousen, "to write" (a book), from Old French composer "put together, compound; adjust, arrange; write" a work (12c.), from com- "with, together" (see com-) + poser "to place," from Late Latin pausare "to cease, lay down" (see pause (n.)).
Meaning influenced in Old French by componere "to arrange, direct" (see composite; also see compound (v.), pose (v.)), which gradually was replaced in French by composer. Similar confusion is found in expose, oppose, repose (v.2), transpose, etc.
Meaning "to make or form by uniting two or more things" is from late 15c. Sense of "be the substance or elements of, make up" is from 1540s. Sense of "invent and put (music) into proper form" is from 1590s. From c. 1600 as "bring into a composed state, to cal, quiet;" from 1650s as "place (parts or elements) in proper form, arrange."
In painting, "combine into an arrangement with artistic effect" (1782). In printing, "put into type" (1630s), but the usual term among printers was set. Related: Composed; composing. The printers' composing room is from 1737.