Mass of silver say, inside jar (9)
I believe the answer is:
aggregate
'mass' is the definition.
(I know that mass can be written as aggregate)
'silver say inside jar' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'inside' indicates putting letters inside.
'jar' becomes 'grate' (make unpleasant sound).
'eg' going within 'grate' is 'gregate'.
'ag'+'gregate'='AGGREGATE'
'of' acts as a link.
(Other definitions for aggregate that I've seen before include "All - broken stone put in cement" , "Sum total" , "Accumulation" , "Collective total - a great egg (anag)" , "Combined or total amount" .)