chessmen (n.)

very ancient game of skill with 32 pieces, played by two on a checkered board of 64 squares, 13c., from Old French esches "chessmen," plural of eschec "game of chess, chessboard; checkmate" (see check (n.1)), so called from the key move of the game. Modern French distinguishes échec "check, blow, rebuff, defeat," from plural échecs "chess."

The original word for "chess" is Sanskrit chaturanga "four members of an army" — elephants, horses, chariots, foot soldiers. This is preserved in Spanish ajedrez, from Arabic (al) shat-ranj, from Persian chatrang, from the Sanskrit word.

The chess pieces are the block alphabet which shapes thoughts; and these thoughts, although making a visual design on the chessboard, express their beauty abstractly, like a poem. [Marcel Duchamp, address to New York State Chess Association, Aug. 30, 1952]

plural of man (n.). In common with German Männer, etc., it shows effects of i-mutation. Used as an indefinite pronoun ("one, people, they") from late Old English. Men's liberation first attested 1970. Men's room "a lavatory for men" is by 1908, American English. Earlier it had a more general sense:

men's room, n. "One end of this [cook and dining] room is partitioned off for a men's room, where the crew sit evenings, smoking, reading, singing, grinding their axes, telling stories, etc., before climbing the ladder to their night's rest in the bunk room ... For many years women have been employed in [logging] camps as cooks, hence the name men's room, for the crew are not allowed in the cook room except at meal time." [quoted in "Some Lumber and Other Words," in Dialect Notes, vol. II, part VI, 1904]

Menswear (also men's wear) "clothes for men" is by 1906. To separate the men from the boys in a figurative sense "distinguish the manly, mature, capable, etc. in a group from the rest" is from 1943; earliest uses tend to credit it to U.S. aviators in World War II.

One of the most expressive G.I. terms to come out of the late strife was "that's where they separate the men from the boys" — so stated by American aviators leaning from their cockpits to observe a beach-landing under fire on some Pacific island far below. ["Arts Magazine," 1947]