Material teacher uses to hem government leader's finery (7)
I believe the answer is:
regalia
'finery' is the definition.
(synonyms)
'material teacher uses to hem government leader's' is the wordplay.
'material teacher uses' becomes 'realia' (realia are real objects used as teaching aids).
'to hem' means one lot of letters goes inside another (hem can mean to enclose).
'leader' indicates taking the first letters.
The first letter of 'government' is 'g'.
'realia' going around 'g' is 'REGALIA'.
(Other definitions for regalia that I've seen before include "Crown and associated pieces" , "Insignia of royalty or office" , "Badges of office" , "Crown, sceptre etc used at a coronation" , "Emblems of royalty used at coronations" .)