Unlawfully take old jerk's automatic (7)
I believe the answer is:
robotic
'automatic' is the definition.
(I know that automatic can be written as robotic)
'unlawfully take old jerk's' is the wordplay.
'unlawfully' becomes 'rob' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'take' means one lot of letters go next to another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'jerk' becomes 'tic' (jerking movement by the body).
'rob'+'o'+'tic'='ROBOTIC'
Can you help me to learn more?
(Other definitions for robotic that I've seen before include "Of mechanical movements" , "Of or using automatons" , "Moving mechanically" , "acting without thinking?" , "Like automatic device" .)