1. Entering into numerous English words, mostly technical, as dichromic, dicotyledon, digamma, digamy, diglot, digraph, dilemma, diphthong, diptych, distich, disyllable; also in the nomenclature of Natural History as Diadelphia, Diandria, Didelphia, Diptera: which see in their alphabetical places. So in Crystallography, as in di-tetrahedron a crystal having twice four sides or planes; so di-hexahedron, etc.