The words "main" and "principal" are very similar and you could use either in almost any context I can think of. The word "main" is more common in everyday use. "Principal" sounds more formal and academic. "Principal" also could carry the idea of being first, whereas "main" does not imply first, just most important. If you have an example of a context you were wondering about, I would be happy to tell you which word sounds better to my native ear.

The words are synonyms, having very similar meanings, and for the most part are interchangeable, though "main" is more often used in everyday speech. I enjoy the old 1828 Webster's Dictionary. His definitions for both words are: Main: Principal; chief; that which has most power in producing an effect, or which is mostly regarded in prospect; as the main branch or tributary stream of a river; the main timbers of an edifice; a main design; a main object. Principal: Chief; highest in rank, character or respectability; as the principal officers of a government; the principal men of a city, town, or state. Most important or considerable; as the principal topics of debate; the principal arguments in a case; the principal points of law; the principal beams of a building; the principal productions of a country.

It's exactly the same. English often has 2 words to express an idea, one has german roots, the other latin roots. I this example. The german one is Main and the latin word is principle. There are plenty of other examples : Fun/amusement Answer/respinse .....

Thank you for this info.

WWW.WEBSTERS1828.COM is the online version. A hard copy can be purchased through Amazon.com for about $66. It is also available with some software programs, like "mysword" and "esword."