Theologian in time becomes parent (5)
I believe the answer is:
daddy
'parent' is the definition.
(I know that parent can be written as daddy)
'theologian in time' is the wordplay.
'theologian' becomes 'DD' (Doctor of Divinity degree).
'in' indicates putting letters inside.
'time' becomes 'day' (day is a kind of time).
'dd' inserted within 'day' is 'DADDY'.
'becomes' acts as a link.
(Other definitions for daddy that I've seen before include "Pa" , "pop" , "Informal father" , "Papa" , "Child's father" .)