Peak in Puerto Rico (3)
I believe the answer is:
tor
'peak' is the definition.
(thesaurus)
'in puerto rico' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TOR' is hidden in the letters of 'puerto rico'.
(Other definitions for tor that I've seen before include "Rocky outcrop" , "Fermenting agent" , "rise" , "It rises" , "Dartmoor peak" .)