Exquisite poem that mourns losing Unknown Soldier (7)
I believe the answer is:
elegant
'exquisite' is the definition.
(similar in meaning)
'poem that mourns losing unknown soldier' is the wordplay.
'poem that mourns' becomes 'elegy'.
'losing' suggests deleting specific letters.
'unknown' becomes 'y' (algebra).
'soldier' becomes 'ant' (soldier is a type of ant).
'elegy' with 'y' taken out is 'eleg'.
'eleg'+'ant'='ELEGANT'
(Other definitions for elegant that I've seen before include "luxurious style?" , "Dignified and graceful" , "Polished" , "Refined and dignified in appearance" , "Chic; smart" .)