a cappella vs critical

a cappella

noun
  • A vocal performance with no instrumental accompaniment. 

adv
  • In a manner of a choir with no instrumental accompaniment; literally, "in the style of the (Sistine) Chapel (in Rome)", such as a musical Mass done a cappella. 

adj
  • Singing solely or mainly without instrumental accompaniment. 

  • Related to a form of purely vocal music mostly associated with American college performance groups. 

critical

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

  • A critical value, factor, etc. 

adj
  • 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. 

  • Extremely important. 

  • 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. 

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