Automaton able to root out a bighead? (5)

I believe the answer is:

robot

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'automaton' is the definition.
(synonyms)

'root out a bighead?' is the wordplay.
'out' indicates putting letters inside.
'a bighead?' becomes 'b' (head letter of 'big').
'root' placed around 'b' is 'ROBOT'.

'able to' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.

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(Other definitions for robot that I've seen before include "Unpaid worker" , "Automated machine" , "Man-made man - man-made machine" , "Programmed machine" , "performer lacking emotion" .)

I've seen this clue in the Evening Standard.

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