Mass held by father in ceremonial splendour (4)
I believe the answer is:
pomp
'ceremonial splendour' is the definition.
(I've seen this before)
'mass held by father' is the wordplay.
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'held by' indicates putting letters inside.
'father' becomes 'pop ' (pop is a kind of father).
'm' put inside 'pop' is 'POMP'.
'in' acts as a link.
(Other definitions for pomp that I've seen before include "Vainglory" , "Stately display, goes with ceremony" , "Self-importance" , "Vain display" , "Grandiosity" .)