Suit for a girl's best friend (8)
I believe the answer is:
diamonds
I believe this clue is a double definition.
'suit' is the first definition.
(I know this)
'a girl's best friend' is the second definition.
(as in the song 'Diamonds Are a Girl's Best Friend')
'for' is the link.
(Other definitions for diamonds that I've seen before include "Pieces of crystalline carbon valued as gems" , "cutters" , "Maids don these gems" , "Components of ring" , "Precious stones found amid nods" .)