Assembled gravesite memorials, essentially, in church yard (8)
I believe the answer is:
cemetery
'assembled gravesite memorials' is the definition.
I can't tell whether this definition defines the answer.
'essentially in church yard' is the wordplay.
'essentially' becomes 'meter' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'church' becomes 'ce' (abbreviation for Church of England).
'yard' becomes 'y' (abbreviation).
'ce'+'y'='cey'
'meter' placed into 'cey' is 'CEMETERY'.
Can you help me to learn more?
(Other definitions for cemetery that I've seen before include "place of mourning" , "Place for burial of bodies" , "place of rest" , "Graveyard" , "Burial ground" .)