A colleague of Castro is hurt (4)
I believe the answer is:
ache
'is hurt' is the definition.
(I've seen this before)
'a colleague of castro' is the wordplay.
'colleague of castro' becomes 'che' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'che'='ACHE'
Can you help me to learn more?
(Other definitions for ache that I've seen before include "Each (anag.)" , "Long ? pain" , "Persistent dull pain" , "Play up" , "painful" .)