"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.
