Unusual setting for garnets (7)
I believe the answer is:
strange
'unusual' is the definition.
(similar in meaning)
'setting for garnets' is the wordplay.
'setting for' indicates an anagram (letters set or arranged differently).
'garnets' with letters rearranged gives 'STRANGE'.
(Other definitions for strange that I've seen before include "Irregular" , "Odd kind of garnets" , "Weird, eerie" , "Odd, peculiar" , "Abnormal" .)