critical vs imperative

critical

adj
  • Extremely important. 

  • Inclined to find fault or criticize. 

  • 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. 

  • Likely to go out of control if disturbed, that is, opposite of stable. 

  • Of the point (in temperature, reagent concentration etc.) where a nuclear or chemical reaction becomes self-sustaining. 

  • 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. 

  • Pertaining to, or indicating, a crisis or turning point. 

noun
  • A critical value, factor, etc. 

  • In breakdancing, a kind of airflare move in which the dancer hops from one hand to the other. 

imperative

adj
  • Essential; crucial; extremely important. 

  • Having semantics that incorporates mutable variables. 

  • Expressing a command; authoritatively or absolutely directive. 

  • Of, or relating to the imperative mood. 

noun
  • A verb in imperative mood. 

  • The grammatical mood expressing an order (see jussive). In English, the imperative form of a verb is the same as that of the bare infinitive. 

  • An essential action, a must: something which is imperative. 

How often have the words critical and imperative occurred in a corpus of books? (source: Google Ngram Viewer )