discoid vs spheroid

discoid

adj
  • Shaped like a disc/disk. 

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

spheroid

adj
  • Of a shape similar to a squashed sphere. 

noun
  • A solid of revolution generated by rotating an ellipse about its major (prolate), or minor (oblate) axis. 

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