A little less than honest politician (5)
I believe the answer is:
trump
'a little' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'less than honest politician' is the wordplay.
'less than' means to remove the last letter (not the full word).
'honest' becomes 'true' (associated in meaning).
'politician' becomes 'mp' (Member of Parliament).
'true' with its last letter taken off is 'tru'.
'tru'+'mp'='TRUMP'
(Other definitions for trump that I've seen before include "Card of the most powerful suit" , "Playing card with designated added value" , "Brick" , "Outdo (with a card?)" , "Surpass" .)