Court getting the king's mistress to return warm wear (7)
I believe the answer is:
woollen
'warm wear' is the definition.
'court getting the king's mistress to return' is the wordplay.
'court' becomes 'woo' (synonyms).
'getting' is a charade indicator (letters next to each other).
'the king's mistress' becomes 'nell'.
'to return' is a reversal indicator.
'nell' in reverse letter order is 'llen'.
'woo'+'llen'='WOOLLEN'
(Other definitions for woollen that I've seen before include "Lone owl (anag)" , "Made from sheep's hair" , "Made of sheep's fleece" , "Like some yarn that's spun" , "Fabric made from the hair of sheep" .)