invalid

Concise Oxford English Dictionary © 2008 Oxford University Press:
invalid1 /ˈɪnvəlɪd/

▶noun a person made weak or disabled by illness or injury. ▶verb (invalids, invaliding, invalided) remove (someone) from active military service because of injury or illness.

■ disable by injury or illness.

– derivatives
invalidism noun.

– origin C17 (as adj. in the sense ‘infirm or disabled’): a special sense of invalid2, with a change of pronunc.

Concise Oxford English Dictionary © 2008 Oxford University Press:
invalid2 /ɪnˈvalɪd/

▶adjective

• 1 not valid or officially recognized.

• 2 not true because based on erroneous information or unsound reasoning.

– derivatives
invalidly adverb.

– origin C16 (earlier than valid): from L. invalidus, from in- ‘not’ + validus (see valid).