critical

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Judging severely and finding fault.
• adjective Relating to or characterized by criticism; reflecting careful analysis and judgment.
• adjective Of, relating to, or characteristic of critics.
• adjective Including scholarly commentary and interpretation.
• adjective Forming or having the nature of a turning point; crucial or decisive: synonym: decisive.
• adjective Medicine Being or relating to a grave physical condition, especially of a patient.
• adjective Being in or verging on a state of crisis or emergency.
• adjective Extremely important or essential: synonym: indispensable.
• adjective Mathematics Of or relating to a point at which a curve has a horizontal tangent line, as at a maximum or minimum.
• adjective Chemistry & Physics Of or relating to the value of a measurement, such as temperature, at which an abrupt change in a quality, property, or state occurs.
• adjective Physics Capable of sustaining a nuclear chain reaction.

from The Century Dictionary.

• Involving judgment as to the truth or merit of something; judicial, especially in respect to literary or artistic works; belonging to the art of a critic; relating to criticism; exercised in criticism.
• Having the knowledge, ability, or discernment to pass accurate judgment, especially upon literary and artistic matters.
• Inclined to make nice distinctions; careful in selection; nicely judicious; exact; fastidious; precise.
• Inclined to find fault or to judge with severity; given to censuring.
• Of the nature of a crisis in affairs; decisive; important as regards consequences: as, a critical juncture.
• In medicine, pertaining to the crisis or turning-point of a disease.
• Formed, situated, or tending to determine or decide; important or essential for determining: as, critical evidence; a critical post.
• Being in a condition of extreme doubt or danger; attended with peril or risk; dangerous; hazardous: as, a critical undertaking.
• In mathematics, relating to the coalescence of different values.
• Distinguished by minute or obscure differences: as, critical species in botany.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Qualified to criticise, or pass judgment upon, literary or artistic productions.
• adjective Pertaining to criticism or the critic's art; of the nature of a criticism; accurate.
• adjective Inclined to make nice distinctions, or to exercise careful judgment and selection; exact; nicely judicious.
• adjective Inclined to criticise or find fault; fastidious; captious; censorious; exacting.
• adjective Characterized by thoroughness and a reference to principles, as becomes a critic.
• adjective Pertaining to, or indicating, a crisis, turning point, or specially important juncture; important as regards consequences; hence, of doubtful issue; attended with risk; dangerous.
• adjective (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.
• adjective the metaphysical system of Kant; -- so called from his most important work, the “Critique of Pure Reason.”

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Inclined to find fault or criticize; fastidious; captious; censorious; exacting.
• adjective Pertaining to, or indicating, a crisis or turning point.
• adjective Extremely important.
• adjective Relating to criticism or careful analysis, such as literary or film criticism.
• adjective medicine Of a patient condition involving unstable vital signs and a prognosis that predicts the condition could worsen; or, a patient condition that requires urgent treatment in an intensive care or critical care medical facility.
• adjective Likely to go out of control if disturbed, that is, opposite of stable.
• adjective Of the point (in temperature, reagent concentration etc.) where a nuclear or chemical reaction becomes self-sustaining.
• noun A critical value, factor, etc.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective forming or having the nature of a turning point or crisis
• adjective of or involving or characteristic of critics or criticism
• adjective urgently needed; absolutely necessary
• adjective at or of a point at which a property or phenomenon suffers an abrupt change especially having enough mass to sustain a chain reaction
• adjective being in or verging on a state of crisis or emergency
• adjective marked by a tendency to find and call attention to errors and flaws
• adjective characterized by careful evaluation and judgment