Main Entry: tran·si·tion

Pronunciation: \tran(t)s-ˈish-ən, tranz-, chiefly British tran(t)s-ˈizh-\

Function: noun

1 : passage from one state or stage to another ; especially : an abrupt change in energy state or level (as of an atomic nucleus or a molecule) usually accompanied by loss or gain of a single quantum of energy
2 : a genetic mutation in RNA or DNA that results from the substitution of one purine base for the other or of one pyrimidine base for the other