au revoir (interj.) 1690s, French, "good-bye for now," literally "to the seeing again." From au "to the" (see au) + revoir "see again, see in turn" (Old French reveoir, 12c.), from Latin revidere, from re- "back, again" (see re-) + videre "to see" (see vision).
blind spot (n.) 1864, "spot within one's range of vision but where one cannot see," from blind (adj.) + spot (n.). Of the point on the retina insensitive to light (where the optic nerve enters the eye), from 1872. Figurative sense (of moral, intellectual, etc. sight) by 1907.