invalid (adj.1)

"not strong, infirm," also "infirm from sickness, disease, or injury", 1640s, from Latin invalidus "not strong, infirm, impotent, feeble, inadequate," from in- "not" (see in- (1)) + validus "strong" (from PIE root *wal- "to be strong"). With pronunciation from French invalide (16c.).

"infirm or sickly person," 1709, originally of disabled military men, from invalid (adj.1). In Paris, Invalides is short for Hôtel des Invalides, home for old and disabled soldiers in the 7th arrondissement of Paris.

"of no legal force," 1630s, from special use of Latin invalidus "not strong, infirm, impotent, feeble, inadequate," from in- "not" (see in- (1)) + validus "strong" (from PIE root *wal- "to be strong").