Thick unpleasant smell above climber (6)
I believe the answer is:
bovine
'thick' is the definition.
(thesaurus)
'unpleasant smell above climber' is the wordplay.
'unpleasant smell' becomes 'BO' (informal abbreviation for body odour).
'above' says to put letters next to each other.
'climber' becomes 'vine' (climbing plant).
'bo'+'vine'='BOVINE'
(Other definitions for bovine that I've seen before include "Resembling cattle" , "Like a cow" , "Relating to cattle" , "Like or to do with cows" , "To do with cows, dull and stupid" .)