Be like a son avoiding mass again (8)
I believe the answer is:
resemble
'be like' is the definition.
(to resemble something is to be like it)
'a son avoiding mass again' is the wordplay.
I cannot quite understand how this works, but
'son' could be 's' (genealogical abbreviation for son) and 's' is found within the answer.
'mass' could be 'm' (symbol used in Physics e.g. f=ma) and 'm' is located in the answer.
'again' could be 're' (prefix meaning 'again') and 're' is located in the answer.
This explanation may well be incorrect...
(Other definitions for resemble that I've seen before include "Appear similar to" , "Possess some similarity to" , "Mirror" , "favour" , "be like or similar to" .)