Old English mawan "to cut (grass, etc.) with a scythe or other sharp instrument" (class VII strong verb; past tense meow, past participle mawen), from Proto-Germanic *mæanan (source also of Middle Low German maeyen, Dutch maaien, Old High German maen, German mähen "to mow," Old English mæd "meadow"), from PIE root *me- (4) "to cut down grass or grain." Related: Mowed; mown; mowing.
"stack of hay," Old English muga, muwa "a heap (of grain, pease, etc.), swath of corn; crowd of people," earlier muha, from Proto-Germanic *mugon (source also of Old Norse mugr "a heap," mostr "crowd"), of uncertain origin. Meaning "place in a barn where hay or sheaves of grain are stored" is by 1755.
early 14c., "one who cuts grass with a scythe," agent noun from mow (v.). Mechanical sense is from 1852.
*mē-, Proto-Indo-European root meaning "to cut down grass or grain." It forms all or part of: aftermath; math (n.2) "a mowing;" mead (n.2) "meadow;" meadow; mow (v.).
It is the hypothetical source of/evidence for its existence is provided by: Greek (poetic) amao, Latin metere "to reap, mow, crop;" Italian mietere, Old Irish meithleorai "reapers," Welsh medi; Old English mawan "to mow," mæd "meadow."
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 *me- (4) "to cut down grass or grain."
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."
When the summer fields are mown,
When the birds are fledged and flown,
And the dry leaves strew the path;
With the falling of the snow,
With the cawing of the crow,
Once again the fields we mow
And gather in the aftermath.
[Longfellow, from "Aftermath"]