Top politician one found in clear (6)
I believe the answer is:
limpid
'clear' is the definition.
('limpid' can be similar in meaning to 'clear')
'top politician one found in' is the wordplay.
'top' becomes 'lid' (lid is a kind of top**).
'politician' becomes 'mp'.
'one' becomes 'i' (Roman numeral).
'found in' is an insertion indicator.
'mp'+'i'='mpi'
'lid' going around 'mpi' is 'LIMPID'.
(Other definitions for limpid that I've seen before include "Clear and transparent, water say" , "Calm" , "'Of liquid, clear and transparent (6)'" , "Crystal-clear" , "Clear and bright" .)