Source : Webster's Revised Unabridged Dictionary (1913)

Functional \Func"tion*al\, a.
   1. Pertaining to, or connected with, a function or duty;
      official.

   2. (Physiol.) Pertaining to the function of an organ or part,
      or to the functions in general.

   {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.

Source : WordNet®

functional
     adj 1: designed for or capable of a particular function or use; "a
            style of writing in which every word is functional";
            "functional architecture" [ant: {nonfunctional}]
     2: involving or affecting function rather than physiology;
        "functional deafness" [ant: {organic}]
     3: relating to or based on function especially as opposed to
        structure; "the problem now is not a constitutional one;
        it is a functional one"; "delegates elected on a
        functional rather than a geographical basis"
     4: fit or ready for use or service; "the toaster was still
        functional even after being dropped"; "the lawnmower is a
        bit rusty but still usable"; "an operational aircraft";
        "the dishwasher is now in working order" [syn: {usable}, {useable},
         {in working order(p)}, {operable}, {operational}]
     5: designed for or adapted to a function or use; "functional
        education selects knowledge that is concrete and usable
        rather than abstract and theoretical"; "functional
        architecture"
     6: (of e.g. a machine) performing or capable of performing; "in
        running (or working) order"; "a functional set of brakes"
        [syn: {running(a)}, {operative}, {working(a)}]

Source : Free On-Line Dictionary of Computing

functional
     
        1. Working correctly.
     
        2. Pertaining to {functional programming}.
     
        3. {higher-order function}.