Softer than velvet? That's rich! (5)
I believe the answer is:
plush
'rich' is the definition.
(similar in meaning)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for plush that I've seen before include "Fabric with a long velvety pile" , "Rich fabric" , "Fabric; richly luxurious" , "Cut pile, softer than velvet" .)