critical

adjective

vitally important
expressing criticism
exercising or involving careful, not not necessarily negative, judgement, often related to art or literature
in grave physical condition (medical)

Wiktionary

Pronunciation: /ˈkɹɪt.ɪ.kəl/ / [ˈkɹɪɾ.ɪ.kəl]

adj

Etymology: Etymology tree Proto-Indo-European *krey- Proto-Indo-European *krinyétider. Proto-Hellenic *kríňňō Ancient Greek κρῑ́νω (krī́nō) Ancient Greek κρῐ- (krĭ-) Proto-Hellenic *-tās Ancient Greek -τής (-tḗs) Ancient Greek κρῐτής (krĭtḗs) Proto-Indo-European *-kos Ancient Greek -κός (-kós) Ancient Greek -ῐκός (-ĭkós) Ancient Greek κριτικός (kritikós)bor. Latin criticus Proto-Indo-European *h₂el-der.? Proto-Italic *-ālis Latin -ālisbor. Old French -albor. ▲ Latin -ālis Old French -elbor. ▲ Latin -ālisbor. Middle English -al English -al English critical From Latin criticus + English -al.

Inclined to find fault or criticize.
“A good teacher is fair but critical.”
“Let us go back to the beginning and consider what the charge is that has made people so critical of me, and has encouraged Meletus to draw up this indictment.”
Pertaining to, or indicating, a crisis or turning point.
“This is a critical moment.”
“Such a scandal as the prosecution of a brother for forgery—with a verdict of guilty—is a most truly horrible, deplorable, fatal thing. It takes the respectability out of a family perhaps at a critical moment, when the family is just assuming the robes of respectability: […] it is a black spot which all the soaps ever advertised could never wash off.”
Extremely important.
“It's critical that you deliver this on time.”
“Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis:[…]. The evolutionary precursor of photosynthesis is still under debate, and a new study sheds light. The critical component of the photosynthetic system is the “water-oxidizing complex”, made up of manganese atoms and a calcium atom.”
Relating to criticism or careful analysis, such as literary or film criticism.
“The movie was a critical success, but bombed at the box-office.”
““Unless you are purchasing cereal from a health food store, many brands that are marketed as healthy are usually full of sugar and processed ingredients,” says Garcia. So when you’re choosing cereal, bread or any other whole-grain product, Garcia recommends reading labels with a critical eye.”
Relating to criticism or careful analysis, such as literary or film criticism.
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.
“The patient's condition is critical.”
In such a condition.
“The patient is critical.”
“Two critical after fatal Wimbledon school crash”
Likely to go out of control if disturbed, that is, opposite of stable.
“The political situation was so critical that the government declared the state of siege.”
Of the point (in temperature, reagent concentration etc.) where a nuclear or chemical reaction becomes self-sustaining.
“The reaction was about to become critical.”
Of a temperature that is equal to the temperature of the critical point of a substance, i.e. the temperature above which the substance cannot be liquefied.
Needing great discrimination to be correctly classified; easily confused.
“critical plants”

noun

A critical value, factor, etc.
“The second undamped system criticals show a greater percentage depression than the first.”
“Finally, criticals are high-risk, high-value items that give the final product a competitive advantage in the marketplace […] Criticals, in part, determine the customer's ultimate cost of using the finished product — in our example, the computer.”
critical hit
In breakdancing, a kind of airflare move in which the dancer hops from one hand to the other.