annular vs discoid

annular

adj
  • Banded or marked with circles. 

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

discoid

adj
  • Shaped like a disc/disk. 

noun
  • A disk-shaped dental excavator designed to remove the carious dentin of a decayed tooth 

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