Undertaking to form union with Liberal hero (4)
I believe the answer is:
idol
'hero' is the definition.
(I've seen this before)
'undertaking to form union with liberal' is the wordplay.
I cannot quite see how this works, but
'liberal' could be 'l' (abbreviation) and 'l' is found in the answer.
The remaining letters 'ido' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for idol that I've seen before include "Object of false worship" , "Person who is the object of intense admiration as by fan club" , "Image of a god (not icon)" , "Someone much loved" , "Graven image or greatly admired person" .)