gumyoudaoicibaDictYouDict[gum 词源字典]
gum: English has three words gum. The oldest, ‘tissue surrounding the teeth’ [OE], originally meant ‘mucous lining of the mouth and throat’; its present-day meaning did not emerge until the 14th century. It is not clear where it came from, although it is related to German gaumen ‘roof of the mouth’, and perhaps to Lithuanian gomurys ‘gum’ and even Latin fauces ‘throat’ (source of English suffocate). Gum ‘sticky material’ [14] comes ultimately from Egyptian kemai, which passed into English via Greek kómmi, Latin cummi or gummi, Vulgar Latin *gumma, and Old French gomme.

And gum in the exclamation by gum [19] is a euphemistic alteration of god.
[gum etymology, gum origin, 英语词源]
gum (n.1)youdaoicibaDictYouDict
c. 1300, "resin from dried sap of plants," from Old French gome "(medicinal) gum, resin," from Late Latin gumma, from Latin gummi, from Greek kommi "gum," from Egyptian kemai. As the name of a hardened, sweetened gelatine mixture as a candy, 1827. As a shortened form of chewing gum, first attested 1842 in American English. The gum tree (1670s) was so called for the resin it exudes. Latin gummi also is the source of German Gummi (13c.).
gum (n.2)youdaoicibaDictYouDict
"soft tissues of the mouth," Old English goma "palate, side of the mouth" (single or plural), from a Germanic source represented by Old Norse gomi "palate," Old High German goumo; related to Lithuanian gomurys "palate," and perhaps from PIE root *gheu- "to yawn" (source also of Old English ginian "to yawn;" see yawn (v.)).
gum (v.1)youdaoicibaDictYouDict
early 14c., gommen, "treat with (medicinal or aromatic) gums," from gum (n.1). In the transferred or figurative sense of "spoil, ruin" (usually with up), as if by some gummy substance, it is first recorded 1901, probably from the notion of machinery becoming clogged. Related: Gummed; gumming.
gum (v.2)youdaoicibaDictYouDict
of infants, toothless adults, etc., "to chew or gnaw (something) with the gums," by 1907, from gum (n.2). Related: Gummed; gumming.