An impasse caused by lifeless hair (8)
I believe the answer is:
deadlock
'an impasse' is the definition.
(I know that impasse can be written as deadlock)
'lifeless hair' is the wordplay.
'lifeless' becomes 'dead' (similar in meaning).
'hair' becomes 'lock' (lock is a kind of hair).
'dead'+'lock'='DEADLOCK'
'caused by' acts as a link.
(Other definitions for deadlock that I've seen before include "Stalemate - impasse" , "Log jam" , "Impasse, standoff" , "Something opened by a key - stalemate" , "Stalemate - it requires a key to open" .)