Treasure intermittently gleams (3)
I believe the answer is:
gem
'treasure' is the definition.
(synonyms)
'intermittently gleams' is the wordplay.
'intermittently' means one should take alternating letters.
The alternating letters of 'gleams' are 'GEM'.
(Other definitions for gem that I've seen before include "Valued person; jewel" , "Pearl" , "Pleasant and cheerful (from German)" , "Half of 7 [SIGN OF THE ZODIAC]" , "A precious stone like a diamond or emerald etc" .)