Sun exclusive -- almost! (3)
I believe the answer is:
sol
'sun' is the definition.
(thesaurus)
'exclusive almost' is the wordplay.
'exclusive' becomes 'sole' ('sole' can be a synonym of 'exclusive').
'almost' means to remove the last letter (most of the word but not all of it).
'sole' with its last letter taken off is 'SOL'.
(Other definitions for sol that I've seen before include "The sun in Spain" , "A Latin sun" , "Note, old french coin" , "Peruvian currency; Roman sun god" , "Spanish and poetic sun" .)