Jewel, a piece of strange matter (3)
I believe the answer is:
gem
'jewel' is the definition.
(synonyms)
'a piece of strange matter' is the wordplay.
'a piece of' says the answer is hidden in the clue.
'GEM' is hidden in the letters of 'strange matter'.
(Other definitions for gem that I've seen before include "Pearl" , "Treasured person" , "perfect specimen" , "one of the Cairngorms?" , "A jewel or precious stone" .)