Impasse with lifeless hair (8)
I believe the answer is:
deadlock
'impasse' is the definition.
(I know that impasse can be written as deadlock)
'with lifeless hair' is the wordplay.
'with' means one lot of letters go next to another.
'lifeless' becomes 'dead' (similar in meaning).
'hair' becomes 'lock' (lock is a kind of hair).
'dead' next to 'lock' is 'DEADLOCK'.
(Other definitions for deadlock that I've seen before include "Something opened by a key - stalemate" , "Log jam" , "Standstill" , "Stalemate - it requires a key to open" , "Stalemate - impasse" .)