what is no3
(redirected from NO3) Also found in: Dictionary, Thesaurus, Medical, Acronyms, Wikipedia. chemical compound containing the nitrate (NO3) radicalradical, in chemistry, group of atoms that are joined together in some particular spatial structure and that take part in most chemical reactions as a single unit. Important inorganic radicals include ammonium, NH4; carbonate, CO3 ; chlorate, ClO3.