a cappella vs motif

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. 

motif

noun
  • A short melodic or lyrical passage that is repeated in several parts of a work. 

  • In a nucleotide or aminoacid sequence, pattern that is widespread and has, or is conjectured to have, a biological significance. 

  • A decorative figure that is repeated in a design or pattern. 

  • A decorative appliqué design or figure, as of lace or velvet, used in trimming. 

  • A basic element of a move in terms of why the piece moves and how it supports the fulfilment of a stipulation. 

  • The physical object or objects repeated at each point of a lattice. Usually atoms or molecules. 

  • A recurring or dominant element; an artistic theme. 

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