Government head (7)
(Other definitions for premier that I've seen before include "First (minister)" , "First in importance" , "man who's in charge" , "Chief minister" , "First in rank or degree" .)
'government head' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for prime minister that I've seen before include "political leader" , "Leader 18 21" , "Government leader" , "First Lord of the Treasury" , "Law once in UK" .)