A great square house, with a heavy portico darkening the principal windows, as its master’s heavy brows overshadowed his eyes.
Went to Westminster School as a King’s Scholar, when I was principally living on garbage, and sleeping in market baskets.
CHAPTER IV — LOST THE robbery at the Bank had not languished before, and did not cease to occupy a front place in the attention of the principal of that establishment now.
He turned from his own class and his own quarter, taking nothing but a little bread as he walked along, towards the hill on which his principal employer lived, in a red house with black outside shutters, green inside blinds, a black street door, up two white steps, BOUNDERBY (in letters very like himself) upon a brazen plate, and a round brazen door-handle underneath it, like a brazen full-stop.
There are no more uses of "principal" in the book.
Show samples from other sources
The principal idea is that decisions should be made by the people who are most knowledgeable about specific circumstances that impact the decision.
The singer was the principal performer; though the whole band was good.