aft vs astern

aft

adv
  • At, near, or towards the stern of a vessel (with the frame of reference within the vessel). 

noun
  • The stern portion of a vessel. 

adj
  • located at the back of a boat, ship, or airplane 

astern

adv
  • Behind (a vessel); in the rear. 

  • In the direction of the stern; backward (motion); to the rear. 

adj
  • Behind a vessel; having a bearing of 180 degrees from ahead. 

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