Graduate elected as principal (4)
I believe the answer is:
main
'principal' is the definition.
('main' can be a synonym of 'principal')
'graduate elected' is the wordplay.
'graduate' becomes 'ma' (abbreviation for Master of Arts).
'elected' becomes 'in'.
'ma'+'in'='MAIN'
'as' is the link.
(Other definitions for main that I've seen before include "Principal sea" , "Chief; sea; pipe" , "Source of electricity" , "Cardinal" , "Principal or high seas" .)