Placed vase that is covering new grave (9)
I believe the answer is:
saturnine
'grave' is the definition.
(saturnine can mean grave or serious)
'placed vase that is covering new' is the wordplay.
'placed' becomes 'sat' (sitting is a kind of placing).
'vase' becomes 'urn' (urn is a kind of vase).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'covering' indicates putting letters inside.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'ie' enclosing 'n' is 'ine'.
'sat'+'urn'+'ine'='SATURNINE'
(Other definitions for saturnine that I've seen before include "Gloomy (temperament)" , "Gloomy; dark and brooding" , "offering little amusement" , "shining? The opposite" , "dour" .)