pluriform vs protean

pluriform

adj
  • Multiform. 

protean

adj
  • Exceedingly variable; readily assuming different shapes or forms. 

noun
  • A protein that has been slightly modified by water, dilute acid, or enzymes, but not modified to the extent of a metaprotein. 

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