a cappella vs singly

a cappella

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. 

noun
  • A vocal performance with no instrumental accompaniment. 

singly

adv
  • In a single or unaccompanied manner; without a companion. 

  • Honestly; sincerely; simply. 

  • Individually; particularly; severally. 

  • Without partners, companions, or associates; single-handed. 

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