Thus top politician conveys his dishonest argument (7)
I believe the answer is:
sophism
'argument' is the definition.
(I have seen 'False argument' mean 'sophism' so perhaps 'argument' could also mean 'sophism')
'thus top politician conveys his dishonest' is the wordplay.
I cannot quite understand how this works, but
'thus' could be 'so' (synonyms) and 'so' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sophism that I've seen before include "faulty reasoning" , "False argument" , "specious argument" .)