Midge has unusual tang (4)
I believe the answer is:
gnat
'midge' is the definition.
(thesaurus)
'unusual tang' is the wordplay.
'unusual' indicates an anagram.
'tang' with letters rearranged gives 'GNAT'.
'has' acts as a link.
(Other definitions for gnat that I've seen before include "a little bit of a nuisance" , "Tang of a biting fly" , "little irritation" , "Small biter" , "small irritant" .)