Solitary soldier without a grave (6)
I believe the answer is:
solemn
'a grave' is the definition.
(I know that grave can be written as solemn)
'solitary soldier without' is the wordplay.
I cannot quite understand how this works, but
'solitary' could be 'sole' (synonyms) and 'sole' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for solemn that I've seen before include "Sober and serious" , "'Earnest, grave (6)'" , "Serious, dignified or ceremonial" , "Portentous" , "Unsmiling" .)