Official law is something completely thoughtless (6)
I believe the answer is:
reflex
'something completely thoughtless' is the definition.
I can't tell whether this defines the answer.
'official law' is the wordplay.
'official' becomes 'ref' (match official in football, say).
'law' becomes 'lex' (Latin for 'law').
'ref'+'lex'='REFLEX'
'is' is the link.
Can you help me to learn more?
(Other definitions for reflex that I've seen before include "Involuntary (action)" , "Action not requiring conscious thought" , "This action is an automatic response to stimulus" , "Unthinking response" , "Involuntary movement" .)