Origin and history of concentrate

late 14c., "middle point of a circle; point round which something revolves," from Old French centre (14c.), from Latin centrum "center," originally the fixed point of the two points of a drafting compass (hence "the center of a circle"), from Greek kentron "sharp point, goad, sting of a wasp," from kentein "stitch," from PIE root *kent- "to prick" (source also of Breton kentr "a spur," Welsh cethr "nail," Old High German hantag "sharp, pointed").

The spelling with -re was popularized in Britain by Johnson's dictionary (following Bailey's), though -er is older and was used by Shakespeare, Milton, and Pope. The meaning "the middle of anything" attested from 1590s. Figuratively, "point of concentration" (of power, etc.), from 1680s. The political use, originally in reference to France, "representatives of moderate views" (between left and right) is from 1837. Center of gravity is recorded from 1650s. Center of attention is from 1868.

1630s, "action of bringing to a center, act of collecting or combining into or about a central point," noun of action from concentrate (v.). Meaning "a mass so collected" is from 1670s; that of "voluntary continuous focusing of mental activity" is from 1825, in phrenology.

Concentration camp is from 1901, originally "compound for noncombatants in a war zone," a controversial idea in the second Boer War (1899-1902). The term emerged with a bad odor.

The concentration camp has now definitely taken its place side by side with the Black Hole of Calcutta as one of those names of horror at which humanity will never cease to shudder. [The Review of Reviews, London, March 1902]

But it also was used 1902 in reference to then-current U.S. policies in the Philippines, and retroactively in reference to Spanish policies in Cuba during the 1896-98 insurrection there. The phrase was used domestically in the U.S. during the Spanish-American war but only in reference to designated rendezvous points for troops headed overseas. In reference to prisons for dissidents and minorities in Nazi Germany from 1934, in Soviet Russia from 1935.