British spice used for muscle (6)
I believe the answer is:
biceps
'for muscle' is the definition.
(biceps is a kind of muscle)
'british spice used' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'used' indicates anagramming the letters.
'spice' with letters rearranged gives 'iceps'.
'b'+'iceps'='BICEPS'
(Other definitions for biceps that I've seen before include "Type of muscle" , "Elbow-bending muscle" , "Contractor" , "Upper-arm muscle" , "Weightlifters use them" .)