Shave around day's start for father (5)
I believe the answer is:
padre
'for father' is the definition.
(synonyms)
'shave around day's start' is the wordplay.
'shave' becomes 'pare' (I've seen this in another clue).
'around' indicates putting letters inside.
'start' suggests taking the first letters.
The initial letter of 'days' is 'd'.
'pare' enclosing 'd' is 'PADRE'.
(Other definitions for padre that I've seen before include "Sky pilot (military slang)" , "clerical worker" , "Priest, chaplain" , "Cleric" , "A military clergyman" .)