Opposite of minor (5)
I believe the answer is:
major
'opposite of minor' is the definition.
('major' is the opposite to 'minor')
This is all the clue.
(Other definitions for major that I've seen before include "Important; old Animal Farm boar" , "See 11 Across" , "Consecrate; thank" , "Important, significant" , "Army officer immediately junior to a lieutenant colonel" .)