Support dodgy lease with highly professional language (8)
I believe the answer is:
legalese
'highly professional language' is the definition.
(jargon used by lawyers)
'support dodgy lease' is the wordplay.
'support' becomes 'leg' (leg is a kind of support).
'dodgy' indicates anagramming the letters (a dodgy or wrong order of the letters).
'lease' is an anagram of 'alese'.
'leg'+'alese'='LEGALESE'
'with' is the link.
(Other definitions for legalese that I've seen before include "contract wording?" , "such language at the bar!" , "barman's peculiar words" , "Special terms" , "formal language" .)