Threadbare soldiers having to return warmth (9)
I believe the answer is:
motheaten
'threadbare' is the definition.
I know nothing about this answer so I can't judge whether this works.
'soldiers having to return warmth' is the wordplay.
'soldiers' becomes 'men' (men can mean a group of soldiers).
'having' means one lot of letters goes inside another.
'return' says the letters should be written backwards.
'warmth' becomes 'heat' (synonyms).
'to' backwards is 'ot'.
'ot'+'heat'='otheat'
'men' placed around 'otheat' is 'MOTHEATEN'.
Can you help me to learn more?
(Another definition for motheaten that I've seen is " Looking shabby".)