c.1200, "to repair," from a shortened form of Old French amender (see amend). Meaning "to put right, atone for, amend (one's life), repent" is from c.1300; that of "to regain health" is from early 15c. Related: Mended; mending.
early 14c., "recompense, reparation," from mend (v.). Meaning "act of mending; a repaired hole or rip in fabric" is from 1888. Phrase on the mend attested from 1802.
Recovering health (1802+)