Emily Dickinson Lexicon

A-BAFT', adv. [or prep. Sax. eft, or æft, again. Hence efter or æfter, after, subsequent; Sax. æftan, behind in place; to which word be is prefixed – beæftan, behind, and this word is corrupted into abaft.]

A sea-term, signifying in or at the hinder part of a ship, or the parts which lie towards the stern; opposed to afore. Relatively it denotes further aft or towards the stern; as, abaft the mainmast. Abaft the beam is in that arch of the horizon which is between a line drawn at right angles with the keel, and the point to which the stern is directed. It is often contracted into aft. – Mar. Dict.