"mouth," 1540s, from Irish gob "mouth," and thus related to the other English noun gob (also see gobbet). Gob-stopper "type of large hard candy" is from 1928.
Entries linking to gob
gobbet n.
late 13c., "a fragment," from Old French gobet "piece, mouthful," diminutive of gobe "mouthful, lump," related to gober "to gulp, swallow down," probably from Gaulish *gobbo- (compare Irish gob "mouth," Gaelic gob "beak").
gab n.
"action of talking," earlier "chatter, loquacity, idle talk" (mid-13c.), also "falsehood, deceit," originally "a gibe, a taunt" (c. 1200), mid-13c., probably from a Scandinavian source akin to Old Norse gabb "mocking, mockery," and in part from Old French gap, gab "joke, jest; bragging talk," which also is probably from Scandinavian (compare gab (v.)). Probably also there is influence from Scottish and northern English gab "the mouth" (see gob (n.2)); OED reports the word "Not in dignified use." Gift of (the) gab "talent for speaking" is from 1680s.