Subsequently less sensible, losing head (5)
I believe the answer is:
after
'subsequently' is the definition.
(I've seen this in another clue)
'less sensible losing head' is the wordplay.
'less sensible' becomes 'dafter' (I've seen this in another clue).
'losing head' means to remove the first letter.
'dafter' with its first letter taken away is 'AFTER'.
(Other definitions for after that I've seen before include "Searching for" , "back along > deck" , "Following, consequent to" , "Following - behind" , "In pursuit of, behind" .)