ahead vs at the back

ahead

adv
  • To a later time. 

  • At an earlier time; beforehand; in advance. 

  • To an earlier time. 

  • In or for the future. 

  • At or towards the front; in the direction one is facing or moving. 

  • So as to be further advanced, either spatially or in an abstract sense. 

at the back

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