Gems for suit (8)
I believe the answer is:
diamonds
I believe this is a double definition.
'gems' is the first definition.
(I know this)
'for suit' is the second definition.
(I've seen this before)
(Other definitions for diamonds that I've seen before include "Quarter-deck" , "rocks?" , "Precious gems" , "In song they're a girl's best friend" , "Precious stones from hard brilliant mineral" .)