What is "functional disease"

Functional \Func"tion*al\ (f[u^][ng]k"sh[u^]n*al), a.

1. Pertaining to, or connected with, a function or duty; official.

2. (Pathology, Physiol.) 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. [WordNet sense 2]

3. Designed for or capable of a particular function or use; as, a style of writing in which every word is functional; functional architecture. [WordNet sense 1]

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.

   Syn: usable, useable, in working order(predicate), operable, operational, running(prenominal), operative.

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.

   Functional disease (Med.), 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.