datum vs missive

datum

noun
  • A premise from which conclusions are drawn. 

  • A floating reference point, or SLDMB, used to evaluate surface currents in a body of water. Often employed by coastal search and rescue. 

  • A fixed reference point or set of reference points which precisely define a system of measurement or a coordinate system. 

  • A fact known from direct observation. 

verb
  • To provide missing data points by using a mathematical model to extrapolate values that are outside the range of a measuring device. 

missive

noun
  • A written message; a letter, note or memo. 

  • Letters sent between two parties in which one makes an offer and the other accepts it. 

adj
  • Specially sent; intended or prepared to be sent. 

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