against vs an

against

prep
  • In competition with, versus. 

  • In contrast or comparison with. 

  • In a contrary direction to. 

  • In front of; before (a background). 

  • Close to, alongside. 

  • In opposition to. 

  • In physical opposition to; in collision with. 

  • As protection from. 

  • Contrary to; in conflict with. 

  • In anticipation of; in preparation for (a particular time, event etc.). 

  • In exchange for. 

  • To be paid now in contrast to the following amount to be paid later under specified circumstances, usually that a movie is made or has started filming. 

  • As counterbalance to. 

  • In physical contact with, so as to abut or be supported by. 

  • Of betting odds, denoting a worse-than-even chance. 

  • As a charge on. 

an

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

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

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. 

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