- (usually before a noun) The principal thing is the main or most important one.
- Canada's principal trading partner is the USA.
- Presumably most of us work for the same principal reason - in order to live.
- (countable) In American English, a principal is the head of a school. (=headmaster in British English)
- (countable) The principal is the most important person in a business, or an artistic group such as a dancers.
- (uncountable) Principal is the money that you borrow and must pay back. It does not include interest.