Acquit Conservative writer and illustrator (5)
I believe the answer is:
clear
'acquit' is the definition.
(I know that acquit can be written as clear)
'conservative writer and illustrator' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'writer and illustrator' becomes 'Lear' (Edward Lear, 1812-1888).
'c'+'lear'='CLEAR'
(Other definitions for clear that I've seen before include "Obvious; remove obstructions from" , "Unimpeded" , "Unambiguous" , "Transparent - free of obstruction" , "Unobstructed" .)