Principally (Adverb)

For the most part; "he is mainly interested in butterflies".

The new employee will principally be working on marketing and sales.
She is a writer, but principally of science fiction novels.
This research is focused principally on adult literacy and employment patterns.
The city's economy is driven principally by its thriving tourism industry.
The country's food supply comes principally from three major crops: rice, wheat, and corn.