adj.1 of or serving a function.
2 (esp. of buildings) designed or intended to be practical rather than attractive; utilitarian.
3 Physiol. a (esp. of disease) of or affecting only the functions of an organ etc., not structural or organic. b (of mental disorder) having no discernible organic cause. c (of an organ) having a function, not functionless or rudimentary.
4 Math. of a function.
Phrases and idioms:
functional group Chem. a group of atoms that determine the reactions of a compound containing the group.
functionality n. functionally adv.