Hence Rees-Mogg & co ring? (4)
I believe the answer is:
ergo
'hence' is the definition.
(I've seen this in another clue)
'rees-mogg co ring?' is the wordplay.
I cannot quite understand how this works, but
'ring?' could be 'go' (ringing is a kind of going) and 'go' is found in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
(Other definitions for ergo that I've seen before include "Therefore (Latin)" , "as a consequence" , "so philosopher wrote in Latin" , "Consequently" , "for this reason" .)