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Used to indicate an alternative, usually only before the last term of a series: hot or cold; this, that, or the other.
(conjunction)
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Used to indicate the second of two alternatives, the first being preceded by either or whether: Your answer is either ingenious or wrong. I didn't know whether to laugh or cry.
(conjunction)
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Archaic Used to indicate the first of two alternatives, with the force of either or whether.
(conjunction)
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Used to indicate a synonymous or equivalent expression: acrophobia, or fear of great heights.
(conjunction)
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Used to indicate uncertainty or indefiniteness: two or three.
(conjunction)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.