impair (v.) Look up impair at Dictionary.com
late 14c., earlier ampayre, apeyre (c.1300), from Old French empeirier (Modern French empirer), from Vulgar Latin *impeiorare "make worse," from assimilated form of in- "into, in" (see in- (2)) + Late Latin peiorare "make worse" (see pejorative). In reference to driving under the influence of alcohol, first recorded 1951 in Canadian English. Related: Impaired; impairing.