Rich in addition to hot-headed (5)
I believe the answer is:
plush
'rich' is the definition.
(similar in meaning)
'addition to hot-headed' is the wordplay.
'addition' becomes 'plus' (I've seen this before).
'to' says to put letters next to each other.
'hot-headed' becomes 'h' (this might be a standard abbreviation of which I'm unaware).
'plus'+'h'='PLUSH'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for plush that I've seen before include "Rich fabric" , "Fabric with a long velvety pile" , "Cut pile, softer than velvet" , "Fabric; richly luxurious" .)