Stern foremost or backward (synset 400277302)
"the steamer went astern at half speed"
At or near or toward the stern of a ship or tail of an airplane (synset 400276839)
"stow the luggage aft"; "ships with square sails sail fairly efficiently with the wind abaft"; "the captain looked astern to see what the fuss was about"
(of a ship or an airplane) behind (synset 400276631)
"we dropped her astern on the end of a seven-inch manilla, and she laid comfortably on the ebb tide"