Dug

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mid 16th century: possibly of Old Norse origin and related to Swedish dägga, Danish dægge ‘suckle’.

wiktionary

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dug

From earlier dugge("pap, teat"; compare also English dialectal ducky, dukky(“the female breast”)), apparently connected to Danish dægge(“to suckle”), Swedish dägga(“to suck”), Old English dēon(“to suckle”). More at doe. Compare doug

etymonline

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dug (n.)

"animal nipple," or, contemptuously, "the human female breast," originally with reference to suckling, 1520s, origin obscure, perhaps related to Swedish dagga, Danish dægge "to suckle."

dug (v.)

past tense and past participle of dig (v.).