quadrumvirate vs quaternion

quadrumvirate

noun
  • Synonym of quattuorvirate. 

quaternion

noun
  • A word of four syllables. 

  • A type of four-dimensional hypercomplex number consisting of a real part and three imaginary parts (real multiples of distinct, independent square roots of −1 denoted by i, j and k); commonly used in vector mathematics and as an alternative to matrix algebra in calculating the rotation of three-dimensional objects. 

  • A group or set of four people or things. 

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