A particle that marks an alternative; as, you may read or may write, that is, you may do one of the things at your pleasure, but not both. It corresponds to either. You may ride either to london or to windsor. It often connects a series of words or propositions, presenting a choice of either; as, he may study law, or medicine, or divinity, or he may enter into trade. If man's convenience, health, Or safety interfere, his rights and claims Are paramount. (Cowper)
Or may be used to join as alternatives terms expressing unlike things or ideas (as, is the orange sour or sweet?), or different terms expressing the same thing or idea; as, this is a sphere, or globe.
Or sometimes begins a sentence. In this case it expresses an alternative or subjoins a clause differing from the foregoing. Or what man is there of you, who, if his son shall ask him for a loaf, will give him a stone? Or for either is archaic or poetic. Maugre thine heed, thou must for indigence Or steal, or beg, or borrow thy dispence. (Chaucer)
Origin: OE. Or, outher, other, auther, either, or, AS. Awer, contr. From ahwaeer; a aye _ hwaeer whether. See Aye, and Whether, and cf. Either.