an vs every

an

noun
  • The first letter of the Georgian alphabet, ა (Mkhedruli), Ⴀ (Asomtavruli) or ⴀ (Nuskhuri). 

prep
  • In each; to or for each; per. 

num
  • one 

article
  • Used before one and words with initial u, eu. 

  • Used before a vowel sound. 

  • Used before all consonants. 

  • Used before /h/ in an unstressed syllable. 

  • Used before /h/ in a stressed syllable. 

every

det
  • All of a countable group (considered individually), without exception. 

  • Denotes equal spacing at a stated interval, or a proportion corresponding to such a spacing. 

  • Denotes an abundance of something. 

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