Twice a year is enough for father (4)
I believe the answer is:
papa
'enough for father' is the definition.
'papa' can be an answer for 'father' (papa is a kind of father). I'm not certain of the 'enough for' bit.
'twice a year' is the wordplay.
'twice' indicates the doubling of some letters.
'a year' becomes 'pa' (per annum).
'pa' duplicated is 'PAPA'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for papa that I've seen before include "Comms code for 'P'" , "Dad" , "The old man" , "Father; letter P" , "Mama's other half?" .)