functional

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Of or relating to a function.
• adjective Of, relating to, or indicating a mathematical function or functions.
• adjective Designed for or adapted to a particular function or use.
• adjective Capable of performing a function; operative.
• adjective Able to function personally or socially despite limitations or impairment.
• adjective Medicine Involving physiological function rather than anatomical structure.
• noun A linear function on vectors whose values are scalars.

from The Century Dictionary.

• Pertaining to functions; relating to some office or function.
• Pertaining to an algebraical operation: as, a functional symbol.
• Having the function usual to the part or organ: as, functional wings of an insect (that is, those used for flying).

from the GNU version of the Collaborative International Dictionary of English.

• adjective Pertaining to, or connected with, a function or duty; official.
• adjective (Pathology, Physiol.) Pertaining to the function of an organ or part, or to the functions in general; involving or affecting function rather than physiology. See functional disease, below.
• adjective Designed for or capable of a particular function or use.
• adjective Fit or ready for use or service; useable; in working order. Antonym of out of order and nonfunctional.
• adjective Designed to emphasize practical utility rather than artistic or aesthetic purposes.
• adjective (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective In good working order.
• adjective Useful; serving a purpose, fulfilling a function
• adjective Only for functional purposes, notably in architecture
• adjective computing theory Having semantics defined purely in terms of mathematical functions, without side-effects.
• adjective medicine Of a disease, such that its symptoms cannot be referred to any appreciable lesion or change of structure; opposed to organic disease, in which the organ itself is affected.
• noun mathematics A function that takes a function as its argument; More precisely: A function y=f(x) whose argument x varies in a space of (real valued, complex valued) functions and whose value belongs to a monodimensional space. An example: the definite integration of integrable real functions in a real interval.
• noun mathematics (functional analysis) A scalar-valued linear function on a vector space
• noun computing An object encapsulating a function pointer (or equivalent).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective (of e.g. a machine) performing or capable of performing
• adjective fit or ready for use or service
• adjective designed for or adapted to a function or use
• adjective involving or affecting function rather than physiology
• adjective designed for or capable of a particular function or use
• adjective relating to or based on function especially as opposed to structure