At retreat, sleep with pain, style (7)
I believe the answer is:
panache
'style' is the definition.
(synonyms)
'at retreat sleep with pain' is the wordplay.
'at' means one lot of letters go next to another.
'retreat' says the letters should be written in reverse.
'sleep with' becomes 'nap' (synonyms. I am not sure about the 'with' bit.).
'pain' becomes 'ache' (ache is a kind of pain).
'nap' in reverse letter order is 'pan'.
'pan' next to 'ache' is 'PANACHE'.
Can you help me to learn more?
(Other definitions for panache that I've seen before include "Sense of style, swagger" , "stylish carriage" , "Dash and verve" , "Swagger, grand manner" , "Flamboyant confidence" .)