Censure engineers over demonstration (7)
I believe the answer is:
reproof
'censure' is the definition.
(I've seen this before)
'engineers over demonstration' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'demonstration' becomes 'proof' (I've seen this in another clue).
're'+'proof'='REPROOF'
(Other definitions for reproof that I've seen before include "Scolding" , "work on raincoat?" , "what mac no longer keeping one dry needs?" , "Castigation" , "Blaming" .)