speed of light, light speed, c -- (the speed at which light travels in a vacuum; the constancy and universality of the speed of light is recognized by defining it to be exactly 299,792,458 meters per second)
vitamin C, C, ascorbic acid -- (a vitamin found in fresh fruits (especially citrus fruits) and vegetables; prevents scurvy)
deoxycytidine monophosphate, C -- (one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose))
cytosine, C -- (a base found in DNA and RNA and derived from pyrimidine; pairs with guanine)
carbon, C, atomic number 6 -- (an abundant nonmetallic tetravalent element occurring in three allotropic forms: amorphous carbon and graphite and diamond; occurs in all organic compounds)