infirm (adj.) Look up infirm at Dictionary.com
late 14c., "weak, unsound" (of things), from Latin infirmus "weak, frail, feeble" (figuratively "superstitious, pusillanimous, inconstant"), from in- "not, opposite of" (see in- (1)) + firmus (see firm (adj.)). Of persons, "not strong, unhealthy," first recorded c.1600. As a noun from 1711.