Webster's Revised Unabridged Dictionary · 1913

Impair

Impair , transitive verb

[Old English empeiren, enpeiren, Old French empeirier, empirier, French empirer, Late Latin impejorare; Latin pref. im- in + pejorare to make worse, from pejor worse. Compare Appair.]

To make worse; to diminish in quantity, value, excellence, or strength; to deteriorate; as, to impair health, character, the mind, value.
Time sensibly all things impairs. — Roscommon
In years he seemed, but not impaired by years. — Pope

Impair , transitive verb

To grow worse; to deteriorate. — Milton

Impair , adjective

[French impair uneven, Latin impar; im- not + par equal.]

Not fit or appropriate. [Obsolete]

Impair , noun

Diminution; injury. [Obsolete]