demarche n.

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

"to walk with measured steps or a regular tread," either individually or as a body, early 15c., from Old French marcher "to stride, march, walk," originally "to trample, tread underfoot," a word of uncertain origin. Perhaps from Frankish *markon or some other Germanic source related to Middle English march (n.) "borderland" (see march (n.2)). Or possibly from Gallo-Roman *marcare, from Latin marcus "hammer," via notion of "tramping the feet."

The transitive meaning "cause to march, cause to move in military order" is from 1590s. Sense of "cause (someone) to go (somewhere) at one's command" is by 1884. Related: Marched; marching. Marching band is attested by 1852. Italian marciare, Spanish marchar are said to be from French.