Astonish a parent with variable English (5)
I believe the answer is:
amaze
'astonish' is the definition.
('amaze' can be a synonym of 'astonish')
'a parent with variable english' is the wordplay.
'parent' becomes 'ma' (ma is a kind of parent).
'with' says to put letters next to each other.
'variable' becomes 'z' (algebra).
'english' becomes 'e' (abbreviation).
'a'+'ma'+'z'+'e'='AMAZE'
(Other definitions for amaze that I've seen before include "Confound with wonder" , "Surprise greatly, astonish" , "baffle" , "Flummox" , "Cause wonder" .)