4. Affording a choice of two or more things, propositions, or courses of action.
5. (Of two things, propositions, or courses) mutually exclusive so that if one is chosen the other must be rejected: The alternative possibilities are neutrality and war.
6. Employing or following nontraditional or unconventional ideas, methods, etc.; existing outside the establishment: an alternative newspaper; alternative lifestyles.
7. Logic. (of a proposition) asserting two or more choices, at least one of which is true.