annular vs discoidal

annular

adj
  • Banded or marked with circles. 

  • Pertaining to, or having the form of, a ring; ring-shaped; in the shape of an annulus. 

discoidal

adj
  • Having the flat, circular shape of a disc or a quoit 

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