early 14c., "fact of being carried on" (as in in process), from Old French proces "a journey; continuation, development; legal trial" (13c.) and directly from Latin processus "a going forward, advance, progress," from past participle stem of procedere "go forward" (see proceed).
Meaning "course or method of action" is from mid-14c.; sense of "continuous series of actions meant to accomplish some result" (the main modern sense) is from 1620s. Legal sense of "course of action of a suit at law" is attested from early 14c.