Critical

1. Qualified to criticise, or pass judgment upon, literary or artistic productions.
2. Pertaining to criticism or the critic's art; of the nature of a criticism; accurate; as, critical knowledge; a critical dissertation.
3. Inclined to make nice distinctions, or to exercise careful judgment and selection; exact; nicely judicious.
4. Inclined to criticise or find fault; fastidious; captious; censorious; exacting.
5. Characterized by thoroughness and a reference to principles, as becomes a critic; as, a critical analysis of a subject.
6. Pertaining to, or indicating, a crisis, turning point, or specially important juncture; important as regards consequences; hence, of doubtful issue; attended with risk; dangerous; as, the critical stage of a fever; a critical situation.
Critical angle (Optics),
that angle of incidence of a luminous ray at which it is wholly reflected, and no portion of it transmitted. The sine of this angle is the reciprocal of the refractive index of the medium.
Critical philosophy ,
the metaphysical system of Kant; -- so called from his most important work, the “Critique of Pure Reason.”