Webster's Revised Unabridged Dictionary · 1913

Functional

Functional (funk"shun*al) , adjective

1.
Pertaining to, or connected with, a function or duty; official.
2.
(Pathology, Physiology) Pertaining to the function of an organ or part, or to the functions in general; involving or affecting function rather than physiology; as, functional deafness; a functional disease. See functional disease, below.
3.
Designed for or capable of a particular function or use; as, a style of writing in which every word is functional; functional architecture.
4.
Fit or ready for use or service; useable; in working order; as, the toaster was still functional even after being dropped; the lawnmower is a bit rusty but still functional. Antonym of out of order and nonfunctional.
5.
Designed to emphasize practical utility rather than artistic or aesthetic purposes; as, functional education selects knowledge that is concrete and usable rather than abstract and theoretical; functional architecture; an amateurish device, crude but functional.
Collocations (1)
Functional disease (Medicine) , a disease of which the symptoms cannot be referred to any appreciable lesion or change of structure; the derangement of an organ arising from a cause, often unknown, external to itself opposed to organic disease, in which the organ itself is affected.