aftermath (n.) Look up aftermath at Dictionary.com
1520s, originally a second crop of grass grown on the same land after the first had been harvested, from after + -math, from Old English mæð "a mowing, cutting of grass," from PIE root *mē- (4) "to cut down grass or grain" (see math (n.2)).

Also known as aftercrop (1560s), aftergrass (1680s), lattermath, fog (n.2). Figurative sense is by 1650s. Compare French regain "aftermath," from re- + Old French gain, gaain "grass which grows in mown meadows," from Frankish or some other Germanic source similar to Old High German weida "grass, pasture."