datum vs letter

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. 

letter

noun
  • Literature. 

  • A size of paper, 215 mm × 280 mm. 

  • A size of paper, 8½ in × 11 in (215.9 mm × 279.4 mm, US paper sizes rounded to the nearest 5 mm). 

  • A symbol in an alphabet. 

  • A division unit of a piece of law marked by a letter of the alphabet. 

  • One who lets, or lets out. 

  • The literal meaning of something, as distinguished from its intended and remoter meaning (the spirit). 

  • A written or printed communication, generally longer and more formal than a note. 

verb
  • To print, inscribe, or paint letters on something. 

  • To earn a varsity letter (award). 

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