Clear one politician wearing hat (6)
I believe the answer is:
limpid
'clear' is the definition.
(similar in meaning)
'one politician wearing hat' is the wordplay.
'one' becomes 'i' (Roman numeral).
'politician' becomes 'MP' (Member of Parliament).
'wearing' is an insertion indicator.
'hat' becomes 'lid' (lid can informally mean a hat).
'i'+'mp'='imp'
'imp' placed within 'lid' is 'LIMPID'.
(Other definitions for limpid that I've seen before include "Calm" , "Translucent" , "Crystal-clear" , "Completely clear" , "Clear - tranquil" .)