1630s, "to bring or come to a common center," from concenter (1590s), from Italian concentrare, from assimilated form of Latin com "with, together" (see con-) + centrum "center" (see center (n.)).

Meaning "condense" is from 1680s; that of "intensify the action of" is from 1758. Sense of "mentally focus" is from 1860s, on the notion of "concentrate the mind or mental powers." Related: Concentrated; concentrating.

"that which has been reduced to a state of purity," 1883, from concentrate(adj.) "reduced to a pure or intense state" (1640s), from concentrate (v.).

"spread or scatter from a point or center," 1879, from de- "do the opposite of" + concentrate (v.). Related: Deconcentrated; deconcentration; deconcentration (1848).

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. 

"gathered into a ball or rounded mass," 1570s, from Latin conglomeratus, past participle of conglomerare "to roll together, concentrate, heap up," from assimilated form of com "with, together" (see con-) + glomerare "to gather into a ball, collect," from glomus (genitive glomeris) "a ball, ball-shaped mass," possibly from PIE *glem- (see glebe).

1590s, transitive, "to form into a ball, to gather into a ball or round body," from Latin conglomeratus, past participle of conglomerare "to roll together, concentrate, heap up," from assimilated form of com "with, together" (see con-) + glomerare "to gather into a ball, collect," from glomus (genitive glomeris) "a ball, ball-shaped mass," possibly from PIE *glem- (see glebe). Intransitive sense of "to come together in a rounded mass" is from 1640s. Related: Conglomerated; conglomerating.

1620s, "act of gathering into a ball or mass," from Late Latin conglomerationem (nominative conglomeratio), noun of action from past participle stem of Latin conglomerare "to roll together, concentrate, heap up," from assimilated form of com "with, together" (see con-) + glomerare "to gather into a ball, collect," from glomus (genitive glomeris) "a ball, ball-shaped mass," possibly from PIE *glem- (see glebe). Meaning "that which is conglomerated" is from 1650s.