Newt (3)
(Other definitions for aft that I've seen before include "Towards the back on board" , "Astern" , "towards the end" , "At the back of a ship" , "Towards rear (of ship)" .)
'newt' is the definition.
(eft is a kind of newt)
This is all the clue.
(Other definitions for eft that I've seen before include "Juvenile twenty-three Ac; rhymes with sinister" , "Slimy creature" , "Juvenile newt" , "Swimmer with feeble legs" , "Kind of newt found in clefts" .)