impair: [14] If to repair something is to ‘put it right’, it seems logical that to impair something should be to ‘make it wrong’. In fact, though, logic has nothing to do with it, for the two words are quite unrelated. Repair comes ultimately from Latin parāre ‘make ready’, whereas impair goes back via Old French empeirier to Vulgar Latin *impējōrāre ‘make worse’.
