Authority shown by teacher, keeping order in middle of seminar (8)
I believe the answer is:
dominion
'authority' is the definition.
(thesaurus)
'teacher keeping order in middle of seminar' is the wordplay.
'teacher' becomes 'don' (don is a kind of teacher).
'keeping' is an insertion indicator.
'order' becomes 'om' (order of merit**).
'middle of' says to take the centre.
The central letter of 'seminar' is 'i'.
'om'+'in'+'i'='omini'
'don' placed around 'omini' is 'DOMINION'.
'shown by' acts as a link.
(Other definitions for dominion that I've seen before include "Authority to rule over and control people" , "territory" , "Government" , "Jurisdiction" , "Sovereignty, control" .)