Principal means main or most important, and can also be the head of a school or a sum of money lent. A principality is a territory ruled by a prince or princess. Think of a prince to remember the second one.
The core difference
Principal is mainly an adjective for something most important, while a principality is a place ruled by a prince or princess.
- principal — main, or the head of a school: Cotton is the region's principal export.
- principality — a region or state headed by a prince or princess: Monaco is a principality.
How to tell them apart
Principal is a working word with several jobs: an adjective meaning most important, a noun for a school head, and a noun for the original sum of money in a loan. A principality is always a place, or occasionally the rank of a ruler.
The two are related, and both trace back to the Latin idea of being first. Because they look alike, people sometimes reach for the longer one to sound formal. If you mean simply main, choose principal.
