Etymology
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outflow (n.)

1869, "act or fact of flowing out, a flowing out or forth;" 1875, "that which flows out," from out- + flow (n.).

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outpouring (n.)

mid-15c., "a pouring out, outflow, effusion," from out- + infinitive of pour (v.). From 1757 as "action of pouring out," probably a re-coinage, originally transferred, of things spiritual; sense of "that which is poured out" (again, usually transferred) is from 1827. A verb, outpour "to pour forth," is attested from 1670s.

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drain (n.)

early 14c., dreine, "passage, pipe, or open channel for the removal of water or other liquid," from drain (v.). From 1721 as "act of draining, gradual or continuous outflow," usually figurative, of money, resources, etc. Colloquial expression down the drain "lost, vanished, gone to waste" is by 1930.

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