Sort of small tiara worn by northern empress (7)
I believe the answer is:
tsarina
'empress' is the definition.
(I've seen this before)
'sort of small tiara worn by northern' is the wordplay.
'sort of' indicates an anagram.
'small' becomes 's' (abbreviation - e.g. clothes size).
'worn by' indicates putting letters inside (I've seen this in other clues).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
's'+'tiara'='stiara'
'stiara' anagrammed gives 'tsaria'.
'tsaria' placed around 'n' is 'TSARINA'.
(Other definitions for tsarina that I've seen before include "Russian noblewoman" , "Nicholas's wife" , "lady of some importance" , "Wife of royal Russian" , "Consort" .)