The Collaborative International Dictionary of English v.0.48:
Criterion \Cri*te"ri*on\ (kr?-t?"r?-?n), n.; pl. Criteria
(-?), sometimes Criterions (-?nz). [Gr. ????? a means for
judging, fr. ???? decider, judge, fr. ????? to separate. See
A standard of judging; any approved or established rule or
test, by which facts, principles opinions, and conduct are
tried in forming a correct judgment respecting them.
Of the diseases of the mind there is no criterion.
Inferences founded on such enduring criteria. --Sir G.
Syn: Standard; measure; rule.