WWotW: Principle vs Principal

I was a little confused today. Actually it does not usually take that much to confuse me. I was handed the business card of a colleague that identified him as a "Principle", rather than a "Principal". It confused me enough that I referred myself to the dictionary to confirm my understanding of both words!

principle noun a basic idea or rule that explains or controls how something happens or works =

principal adjective first in order of importance =