the GNU version of the Collaborative International Dictionary of English
n. Lack of validity or cogency; lack of legal force or efficacy; invalidness.
n. Lack of health; infirmity.
The Century Dictionary and Cyclopedia
n. Weakness; infirmity.
n. Lack of validity; want of cogency, force, or efficacy; specifically, lack of legal force: as, the invalidity of an argument or of a will.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. illogicality as a consequence of having a conclusion that does not follow from the premisses
Word Usage
"Thirdly, claiming invalidity is not as easy as the Conservatives would have us believe, and implies that the medical profession are just giving sick notes away, willy-nilly."