Steal books for mechanical man (5)
I believe the answer is:
robot
'mechanical man' is the definition.
(I've seen this before)
'steal books' is the wordplay.
'steal' becomes 'rob' (robbing is a kind of stealing).
'books' becomes 'ot' (Old Testament).
'rob'+'ot'='ROBOT'
'for' acts as a link.
(Other definitions for robot that I've seen before include "Automated machine" , "Humanoid machine" , "Programmable machine" , "Automatic machine" , "Automation" .)