component

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

• noun A constituent element, as of a system. synonym: element.
• noun A part of a mechanical or electrical complex.
• noun Mathematics One of a set of two or more vectors having a sum equal to a given vector.
• adjective Being or functioning as a constituent or an ingredient.

from The Century Dictionary.

• Composing; constituent; entering into the composition of.
• noun A constituent part: as, quartz, feldspar, and mica are the components of granite.
• noun In mech., one of the parts of a strain, velocity, acceleration, force, etc., out of which the whole may be compounded by the principle of the parallelogram of forces, etc.—that is, by geometrical addition. See composition of forces (under composition), parallelogram of forces (under force), and resolution.
• noun A part of a whole which is so combined with other parts as to modify its distinctive character; especially, in logic, an internal part or part of comprehension; a notion contained in a complex notion.

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

• adjective Serving, or helping, to form; composing; constituting; constituent.
• noun A constituent part; an ingredient.
• noun (Mech.) a force which, acting conjointly with one or more forces, produces the effect of a single force or resultant; one of a number of forces into which a single force may be resolved.

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

• noun A smaller, self-contained part of a larger entity. Often refers to a manufactured object that is part of a larger device.
• adjective Making up a larger whole; as a component word.
• adjective Made up of smaller complete units in combination; as a component stereo.

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

• noun an artifact that is one of the individual parts of which a composite entity is made up; especially a part that can be separated from or attached to a system
• noun something determined in relation to something that includes it
• noun an abstract part of something