Golly

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late 18th century: euphemism for God.

wiktionary

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Euphemism for God, dating from the 18th century. Possibly a compaction of “God′s body”.

From golliwog.

Nonstandard diminutive of galosh.

Possibly from Goliath.This etymology is incomplete. You can help Wiktionary by elaborating on the origins of this term.

etymonline

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golly (interj.)

euphemism for God, by 1775, in Gilbert White's journal; he refers to it as "a sort of jolly kind of oath, or asseveration much in use among our carters, & the lowest people."