to make or cause to become worse; diminish in ability, value, excellence, etc.; weaken or damage

to impair one's health; to impair negotiations.

to grow or become worse; lessen.

Archaic . impairment.

verb

aid , assist , help

verb

blemish , blunt , cheapen , damage , debase , debilitate , decrease , destroy , deteriorate , devaluate , devalue , diminish , ding * , disqualify , enervate , enfeeble , hurt , injure , invalidate , lessen , lose strength , make useless , mar , prejudice , queer , reduce , rough up * , spoil , tarnish , total , tweak , undermine , unfit , vitiate , weaken , worsen , detract from , disserve , flaw , harm , afflict , cripple , hinder , impede , undercut