Is Peru intent on becoming thinner (10)
I believe the answer is:
turpentine
'thinner' is the definition.
(thesaurus)
'is peru intent on becoming' is the wordplay.
'on' is a charade indicator (letters next to each other).
'becoming' indicates an anagram.
'peru' put after 'intent' is 'intentperu'.
'intentperu' is an anagram of 'TURPENTINE'.
(Other definitions for turpentine that I've seen before include "Solvent" , "Oil used in varnishes" , "artist's stuff" , "Oil used in mixing paints" , "Thick, oily resin used as paint thinner" .)