Duff

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mid 19th century: northern English form of dough.

wiktionary

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Representing a northern England and Scots pronunciation of dough.

Origin uncertain; probably related to Proto-Indo-European *dʰewbʰ-(“to whisk, smoke, darken, obscure”).

Origin uncertain; perhaps the same as Etymology 1, above.

Originally thieves' slang; probably a back-formation from duffer.

duff (plural duffs)

etymonline

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duff (n.)

"buttocks, rump," 1830s, of unknown origin. The word had a variety of colloquial, slang, or provincial senses late 18c.-early 19c., some of them at least probably related: "dough," also "stiff flour pudding" (nautical, 1840); something worthless or spurious (1781).