Di- (?). [Gr. dis- twice; akin to &unr_; two, L. bis twice. See Two, and cf. Bi-, Dia-. The L. pref. dis- sometimes assumes the form di-. See Dis-.] A prefix, signifying twofold, double, twice; (Chem.) denoting two atoms, radicals, groups, or equivalents, as the case may be. See Bi-, 2.