Son in church from that time onward (5)
I believe the answer is:
since
'from that time onward' is the definition.
'since' can be an answer for 'from' (I've seen this in another clue). I am unsure of the remainder of the definition.
'son in church' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'church' becomes 'CE' (abbreviation for Church of England).
's'+'in'+'ce'='SINCE'
Can you help me to learn more?
(Other definitions for since that I've seen before include "in the past" , "Seeing that" , "Because; ago" , "From that time one" .)