thymine [thymines]◼◼◼(organic chemistry, genetics: heterocyclic base, 5-methylpyrimidine-2,4(1H,3H)-dione) noun [UK: θˈaɪmaɪn] [US: θˈaɪmaɪn]DNA is composed of four nucleotides: adenine, thymine, cytosine and guanine. = L'ADN est composé de quatre nucléotides : adénine, thymine, cytosine et guanine.