chemical element, element - any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter

iodine-131 - heavy radioactive isotope of iodine with a half-life of 8 days; used in a sodium salt to diagnose thyroid disease and to treat goiter

iodine-125 - light radioactive isotope of iodine with a half-life of 60 days; used as a tracer in thyroid studies and as a treatment for hyperthyroidism

halogen - any of five related nonmetallic elements (fluorine or chlorine or bromine or iodine or astatine) that are all monovalent and readily form negative ions

brine, saltwater, seawater - water containing salts; "the water in the ocean is all saltwater"

digit, figure - one of the elements that collectively form a system of numbers; "0 and 1 are digits"

monas, monad - a singular metaphysical entity from which material properties are said to derive

singleton - a single object (as distinguished from a pair)

Latin alphabet, Roman alphabet - the alphabet evolved by the ancient Romans which serves for writing most of the languages of western Europe

alphabetic character, letter of the alphabet, letter - the conventional characters of the alphabet used to represent speech; "his grandmother taught him his letters"

cardinal - being or denoting a numerical quantity but not order; "cardinal numbers"