Gash
Middle English garse, from Old French garcer ‘to chap, crack’, perhaps based on Greek kharassein ‘sharpen, scratch, engrave’. The current spelling is recorded from the mid 16th century.
wiktionary
Alteration of older garsh, from Middle English garsen, from Old French garser, jarsier (Modern French gercer), from Vulgar Latin *charaxāre, from Ancient Greek χαρακτήρ(kharaktḗr, “engraver”).
From ghastful, by association with gash.
etymonline
gash (n.)
1540s, alteration of Middle English garce "a gash, cut, wound, incision" (early 13c.), from Old North French garser "to scarify, cut, slash" (Old French *garse), apparently from Vulgar Latin *charassare, from Greek kharassein "engrave, sharpen, carve, cut," from PIE *gher- (4) "to scrape, scratch" (see character). Loss of -r- is characteristic (see ass (n.2)). Slang use for "vulva" dates to mid-1700s. Provincial English has a set of words (gashly, gashful, etc.) with forms from gash but senses from gast- "dreadful, frightful."
gash (v.)
1560s, alteration of older garsh, from Middle English garsen (late 14c.), from Old North French garser "to cut, slash" (see gash (n.)). For loss of -r-, see ass (n.2). Related: Gashed; gashing.
