to make or cause to become worse; diminish in ability, value, excellence, etc.; weaken or damage:
to impair one's health; to impair negotiations.
verb (used without object)
to grow or become worse; lessen.
1250-1300;Middle Englishempairen, empeiren to make worse < Middle Frenchempeirer, equivalent to em-im-1 + peirer to make worse < Late Latinpējōrāre, equivalent to Latinpējōr-, stem of pējor worse + -ā- thematic vowel + -re infinitive suffix; cf. pejorative
late 14c., earlier ampayre, apeyre (c.1300), from O.Fr. empeirier, from V.L. *impejorare "make worse," from L. in- "into" + L.L. pejorare "make worse," from pejor "worse." In ref. to driving under the influence of alcohol, first recorded 1951 in Canadian Eng.