Hide unwritten poetry in the heart (7)
I believe the answer is:
blanket
'hide' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for blanket that I've seen before include "Warm covering" , "warmer" , "Warm item of bedding" , "Cover with a thick layer" , "Comprehensive" .)