Origin of bigger machine (4)
I believe the answer is:
germ
'origin' is the definition.
(germ is a kind of origin)
'of bigger machine' is the wordplay.
'of' indicates the answer is hidden within the clue.
'GERM' is hidden within 'bigger machine'.
(Other definitions for germ that I've seen before include "Start of an idea" , "Shoot" , "Micro-organism that causes disease" , "Minute life form" , "starting point" .)