a. 1. Pertaining to, or connected with, a function or duty; official. [ 1913 Webster ]

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. [ wns=2 ] [ 1913 Webster ]

3. Designed for or capable of a particular function or use; as, a style of writing in which every word is functional; functional architecture. [ wns=1 ] [ WordNet 1.6 ]

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. [ wns=4 & 6 ]
Syn. -- usable, useable, in working order(predicate), operable, operational, running(prenominal), operative. [ WordNet 1.6 ]

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. [ WordNet 1.6 ]

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. [ 1913 Webster ]

n. 1. a psychology based on the assumption that all mental process are useful to an organism in adapting to the environment. [ WordNet 1.5 ]

2. any doctrine that stresses utility or purpose. [ WordNet 1.5 ]

n. an adherent of functionalism. [ WordNet 1.5 ]

v. t. To assign to some function or office. [ R. ] [ 1913 Webster ]

adv. In a functional manner; as regards normal or appropriate activity. [ 1913 Webster ]

The organ is said to be functionally disordered. Lawrence. [ 1913 Webster ]