a cappella vs act

a cappella

noun
  • A vocal performance with no instrumental accompaniment. 

adj
  • Singing solely or mainly without instrumental accompaniment. 

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

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. 

act

noun
  • A division of a theatrical performance. 

  • A product of a legislative body, a statute. 

  • A display of behaviour. 

  • A display of behaviour meant to deceive. 

  • Something done once and for all, as distinguished from a work. 

  • Any organized activity. 

  • A performer or performers in a show. 

  • A formal or official record of something done. 

  • The process of doing something. 

  • A thesis maintained in public, in some English universities, by a candidate for a degree, or to show the proficiency of a student. 

  • Something done, a deed. 

verb
  • Of a play: to be acted out (well or badly). 

  • To perform a theatrical role. 

  • To play (a role). 

  • To convey an appearance of being. 

  • To map via a homomorphism to a group of automorphisms (of). 

  • To feign. 

  • To do something. 

  • To have an effect (on). 

  • To behave in a certain manner for an indefinite length of time. 

  • To do something that causes a change binding on the doer. 

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