Detest pillbox, for example, on top of embankment (4)
I believe the answer is:
hate
'detest' is the definition.
('hate' can be a synonym of 'detest')
'pillbox for example on top of embankment' is the wordplay.
'pillbox for example' becomes 'hat' (pillbox is a kind of hat**).
'on top of' indicates taking the first letters (I've seen 'on top' mean this).
The initial letter of 'embankment' is 'e'.
'hat'+'e'='HATE'
(Other definitions for hate that I've seen before include "Fury" , "Intense emotion opposite to love" , "Antipathy" , "[OPPOSITE OF] Be besotted with" , "Passionately dislike" .)