impair (v.)

late 14c., a re-Latinizing of earlier ampayre, apeyre "make worse, cause to deteriorate" (c. 1300), from Old French empeirier "make worse" (Modern French empirer), from Vulgar Latin *impeiorare "make worse," from assimilated form of in- "into, in" (from PIE root *en "in") + Late Latin peiorare "make worse," from peior "worse," perhaps originally "stumbling," from PIE *ped-yos-, suffixed (comparative) of *ped- "to walk, stumble, impair," from root *ped- "foot. In reference to driving under the influence of alcohol, first recorded 1951 in Canadian English. Related: Impaired; impairing.