Commander barking mad, terrible liar (7)
I believe the answer is:
admiral
'commander' is the definition.
(thesaurus)
'barking mad terrible liar' is the wordplay.
'barking' indicates an anagram ('barking' can informally mean mad).
'terrible' indicates anagramming the letters.
'mad' with letters rearranged gives 'adm'.
'liar' is an anagram of 'iral'.
'adm'+'iral'='ADMIRAL'
(Other definitions for admiral that I've seen before include "Naval chief" , "Navy rank" , "Senior officer; mad liar (anag.)" , "Senior naval officer" , "Eg, Nelson" .)