gathering vs tetrad

gathering

noun
  • A group of people or things. 

  • A meeting or get-together; a party or social function. 

  • A section, a group of bifolios, or sheets of paper, stacked together and folded in half. 

  • The collection of produce, items, goods, etc.; the practice of collecting food from nature. 

  • A tumor or boil suppurated or maturated; an abscess. 

  • A charitable contribution; a collection. 

adj
  • That gathers together. 

tetrad

noun
  • A group of four things. 

  • A unit of land area of two by two (that is, four) square kilometres. 

  • A group of four basis vectors for a four-dimensional manifold in differential geometry. 

  • A group of four haploid and immature pollen grains in tetrahedral fashion produced by meiotic microsporogenesis. 

  • Two pairs of sister chromatids (a dyad pair) aligned in a certain way and often on the equatorial plane during the meiosis process. 

  • A tetravalent atom or radical. 

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