Radio is crook (8)
I believe the answer is:
receiver
This clue might be a double definition.
'radio' is the first definition.
(thesaurus)
'crook' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'is' acts as a link.
Can you help me to learn more?
(Other definitions for receiver that I've seen before include "Beneficiary; fence" , "Legally-appointed person to liquidate or preserve assets" , "wide one perhaps" , "Person appointed to liquidate or preserve assets" , "Equipment used to ring" .)