Intelligent former Liberal Democrat leader caught out (4)
I believe the answer is:
able
'intelligent' is the definition.
(thesaurus)
'former liberal democrat leader caught out' is the wordplay.
'former liberal democrat leader' becomes 'Cable' (former leader of the Liberal Democrats Vince Cable).
'caught' becomes 'c' (cricket abbreviation).
'out' indicates named letters should be taken away.
'cable' with 'c' taken out is 'ABLE'.
(Other definitions for able that I've seen before include "Competent and equipped" , "In a position or competent to" , "Bale out, being competent" , "Qualified - expert" , "Fully competent" .)