"confused, dazed, stupid, tipsy," 1720s, perhaps from mossy, or from dialectal mosey (adj.) "moldy, hazy; stupefied with drink, dull, stupid."
"one easily deceived or led astray by false representations," 1680s, from French dupe "deceived person," from duppe (early 15c.), thieves' jargon, perhaps from phrase de huppe "of the hoopoe," an extravagantly crested and reputedly stupid bird. For names of supposedly stupid birds applied to stupid persons, compare booby, goose (n.), gull (n.2) .
"dull, stupid fellow," 1540s, perhaps a variant of dold "dull, foolish" (mid-15c.), influenced by dulte, dolte, past-participle forms of Middle English dullen "to dull; make or become dazed or stupid" (see dull (v.)). Related: Doltish "foolish, stupid" (1540s); doltishly; doltishness.