Lemons thrown in grave (6)
I believe the answer is:
solemn
'grave' is the definition.
(synonyms)
'lemons thrown' is the wordplay.
'thrown' indicates anagramming the letters.
'lemons' is an anagram of 'SOLEMN'.
'in' is the link.
(Other definitions for solemn that I've seen before include "Formal, ceremonial" , "Serious, dignified or ceremonial" , "Portentous" , "Serious; deeply sincere" , "Formal, ceremonius" .)