astern vs abaft

astern and abaft both are adverbs.

Word	Noun	Adjective	Verb	Adverb
astern	No	No	No	Yes
abaft	No	No	No	Yes

As adverbs, astern and abaft are synonyms defined as:

astern and abaft: at or near or toward the stern of a ship or tail of an airplane

Other synonyms of astern include aft.

astern (adverb)	abaft (adverb)
(of a ship or an airplane) behind	at or near or toward the stern of a ship or tail of an airplane
at or near or toward the stern of a ship or tail of an airplane
stern foremost or backward