[1. Symbol for the vitamin D potency of cod liver oil, multiples of which (5D, 100D) are used to designate the vitamin D potency of irradiated ergosterol (viosterol) or other substances. Also, symbol for deuterium; dihydrouridine in nucleic acids; diffusing capacity; aspartic acid; diffusion coefficient (in italics).2. In optics, abbreviation for diopter, or dexter (L. right).3. In electrodiagnosis, abbreviation for duration, the current that is flowing and the circuit that is being closed.4. In dental formulas, abbreviation for deciduous2.5. As a subscript, refers to dead space.6. D line in Na emission spectra.