Not valid; not true, correct, acceptable or appropriate.
Suffering from disability or illness.
Intended for use by an invalid.
To make invalid or affect with disease.
To exempt from (often military) duty because of injury or ill health.
Not rational; unfounded or nonsensical.
Of a real number, that cannot be written as the ratio of two integers.
A real number that can not be expressed as the quotient of two integers, an irrational number.