letter vs text file

letter

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

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

  • Literature. 

  • 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). 

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

  • To earn a varsity letter (award). 

text file

noun
  • A data file containing only plain, human-readable text, distinct from documents with embedded formatting 

  • A data file in a character encoding that allows it to be read in non-specialised text editor. 

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