extent vs semidiameter

extent

noun
  • The space, area, volume, etc., to which something extends. 

  • A former tent; something (or someone) that was a tent but no longer is 

  • The valuation of property. 

  • A range of values or locations. 

  • A contiguous area of storage in a file system. 

  • A writ directing the sheriff to seize the property of a debtor, for the recovery of debts of record due to the Crown. 

semidiameter

noun
  • The apparent radius of a star etc, when viewed from Earth. 

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