From The Collaborative International Dictionary of English v.0.48:
Mump \Mump\, v. t. [imp. & p. p. Mumped; p. pr. & vb. n.
Mumping.]
1. To utter imperfectly, brokenly, or feebly.
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Old men who mump their passion. --Goldsmith.
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2. To work over with the mouth; to mumble; as, to mump food.
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3. To deprive of (something) by cheating; to impose upon.
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