Father's the titular head no longer (4)
I believe the answer is:
past
'no longer' is the definition.
'father's the titular head' is the wordplay.
'father's' becomes 'pa's' (pa can mean dad or father).
'head' says to take the initial letters.
The first letter of 'titular' is 't'.
'pas'+'t'='PAST'
(Other definitions for past that I've seen before include "historical times" , "The time that has elapsed" , "Days gone by" , "over and done with" , "Finished, gone" .)