Touched, dead astern (4)
I believe the answer is:
daft
'touched' is the definition.
(thesaurus)
'dead astern' is the wordplay.
'dead' becomes 'd'.
'astern' becomes 'aft' (I've seen this before).
'd'+'aft'='DAFT'
(Other definitions for daft that I've seen before include "Bats!" , "Potty" , "Scatty" , "'Silly, foolish (4)'" , "Informally silly or foolish" .)