gendarme (n.)

[weapon], c. 1300, armes (plural) "weapons of a warrior," from Old French armes (plural), "arms, weapons; war, warfare" (11c.), from Latin arma "weapons" (including armor), literally "tools, implements (of war)," from PIE *ar(ə)mo-, suffixed form of root *ar- "to fit together." The notion seems to be "that which is fitted together." Compare arm (n.1).

The meaning "branch of military service" is from 1798, hence "branch of any organization" (by 1952). The meaning "heraldic insignia" (in coat of arms, etc.) is early 14c., from a use in Old French; originally they were borne on shields of fully armed knights or barons. To be up in arms figuratively is from 1704; to bear arms "do military service" is by 1640s.

"toilet," 1932, probably from jakes, used for "toilet" since 15c. Meaning "prostitute's customer" is from 1911, probably from the common, and thus anonymous, name by which they identified themselves. Meaning "policeman" is by 1901, from shortening of johndarm (1823), a jocular Englishing of gendarme.

"John Darm! who's he?" "What, don't you know!

In Paris he is all the go;

Like money here,—he's every thing;

A demigod—at least a king!

You cannot fight, you cannot drink,

Nor have a spree, nor hardly think,

For fear you should create a charm,

To conjure up the fiend John Darm!

["John Darm," in "Varieties in Verse," John Ogden, London, 1823]