Insignificant worker (3)
I believe the answer is:
cog
'insignificant worker' is the definition.
(a cog in a machine)
This is the entire clue.
(Other definitions for cog that I've seen before include "one engaged in revolutionary activity" , "Minor person in organisation" , "Each of series of teeth on wheel" , "Junior official" , "Tooth on gearwheel" .)