Huge number working beyond factory unit (7)
I believe the answer is:
million
'huge number' is the definition.
(a million is a huge number)
'working beyond factory unit' is the wordplay.
'working' becomes 'on' (on can mean working or activated).
'beyond' is a charade indicator (letters next to each other).
'factory' becomes 'mill' (mill is a type of factory).
'unit' becomes 'I' (resembles 1, a unit).
'mill'+'i'='milli'
'on' put after 'milli' is 'MILLION'.
(Other definitions for million that I've seen before include "Ten to the power of six" , "A thousand thousnad" , "What mega means" , "A thousand thousands" , "fortune!" .)