alternative

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

• noun One of a number of possible choices or courses of action.
• noun A choice or course of action that is mutually exclusive with another: synonym: choice.
• noun A situation presenting a choice between two mutually exclusive possibilities.
• adjective Being one of a number of possible choices or courses of action.
• adjective Being one of two mutually exclusive choices or courses of action.
• adjective Substitute or other.
• adjective Existing outside traditional or established institutions or systems.
• adjective Espousing or reflecting values that are different from those of the establishment or mainstream.

from The Century Dictionary.

• Of two things, such that only one can be selected or only one is possible, etc.; mutually exclusive.
• Affording a choice between two things, or a possibility of one thing out of two; given or offered for selection, as against something else: as, an alternative proposition; he presented an alternative statement.
• Alternate; reciprocal. Holland.
• In botany, having the parts of the inner whorl alternate with the outer: applied to the estivation or arrangement of the parts of the perianth in the bud.
• noun A choice between two things; a possibility of one of two things.
• noun One of two things of which either is possible or may be chosen.
• noun In the Roman Catholic Church, an arrangement by which the pope nominates to vacant benefices only in alternate months, at other times leaving the nomination to the bishop of the diocese or to the regular patron. The month counted is that in which the benefice becomes vacant.

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

• noun An offer of two things, one of which may be chosen, but not both; a choice between two things, so that if one is taken, the other must be left.
• noun Either of two things or propositions offered to one's choice. Thus when two things offer a choice of one only, the two things are called alternatives.
• noun The course of action or the thing offered in place of another.
• noun A choice between more than two things; one of several things offered to choose among.
• adjective Offering a choice of two things.
• adjective Disjunctive.
• adjective obsolete Alternate; reciprocal.

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

• adjective Relating to a choice between two or more possibilities
• adjective Not traditional, outside the mainstream, underground (e.g., alternative medicine, alternative lifestyle, alternative rock).
• adjective this sense?) Other.

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

• adjective serving or used in place of another
• adjective pertaining to unconventional choices
• adjective necessitating a choice between mutually exclusive possibilities
• noun one of a number of things from which only one can be chosen