Engineer, eh? So it's said (4)
I believe the answer is:
watt
'engineer' is the definition.
(I know that Watt is a engineer)
'eh? so it's said' is the wordplay.
'eh?' becomes 'what' ('eh' can mean 'pardon' or 'what').
'so it's said' shows a homophone (sound like).
'what' is a homophone of 'WATT'.
(Other definitions for watt that I've seen before include "James - - (Scottish inventor)" , "Worker in steam" , "Unit of electric power" , "man of power?" , "Unit of electricity" .)