astern vs rearward

astern

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

  • Behind (a vessel); in the rear. 

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

rearward

adv
  • Toward the back or rear of something. 

noun
  • The last troop; the rear of an army; a rear guard. 

  • The part that comes last or is situated in the rear; conclusion, wind-up. 

adj
  • Toward the back or rear of something. 

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