trapezium vs trapezoid

trapezium

noun
  • The trapezium bone of the wrist. 

  • A region on the ventral side of the brain, either just back of the pons Varolii, or, as in man, covered by the posterior extension of its transverse fibers. 

  • A quadrilateral with two sides parallel and two sides non-parallel. 

  • A quadrilateral with two sides parallel. 

trapezoid

noun
  • The trapezoid bone of the wrist. 

  • A (convex) quadrilateral with two (non-adjacent) parallel sides. 

  • A convex quadrilateral with no sides parallel. 

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