or 1 (ôr; ər when unstressed)
a. Used to indicate an alternative, usually only before the last term of a series: hot or cold; this, that, or the other.
b. 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.
c. Archaic Used to indicate the first of two alternatives, with the force of either or whether.
2. Used to indicate a synonymous or equivalent expression: acrophobia, or fear of great heights.
3. Used to indicate uncertainty or indefiniteness: two or three.
[Middle English, from other, or (from Old English, from oththe) and from outher (from Old English āhwæther, āther; see EITHER).]
Usage Note: When all the elements in a series connected by or are singular, the verb they govern is singular: Tom or Jack is coming. Beer, ale, or wine is included in the charge. When all the elements are plural, the verb is plural. When the elements do not agree in number, some grammarians have suggested that the verb should agree in number with the nearest element: Tom or his sisters are coming. The girls or their brother is coming. Cold symptoms or headache is the usual first sign. Other grammarians, however, have argued that such constructions are inherently illogical and that the only solution is to revise the sentence to avoid the problem of agreement: Either Tom is coming or his sisters are. The usual first sign may be either cold symptoms or a headache. See Usage Notes at and/or, either, neither, nor1.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.