Толковый словарь английского языка Oxford English Reference

1. n. (also d) (pl. Ds or D's) 1 the fourth letter of the alphabet. 2 Mus. the second note of the diatonic scale of C major. 3 (as a Roman numeral) 500. 4 = DEE. 5 the fourth highest class or category (of academic marks etc.). 2. symb. Chem. the element deuterium. 3. abbr. (also D.) 1 US Democrat. 2 dimension (3-D). D v. colloq. (usu. after pronouns) had, would (I'd; he'd). Etymology: abbr.