All 4 Uses of

principal
in
Through the Looking-Glass

And Alice got the Red Queen off the table, and set it up before the kitten as a model for it to imitate: however, the thing didn't succeed, principally, Alice said, because the kitten wouldn't fold its arms properly.†
Chpt 1

principally = primarily or most importantly

'Principal rivers—there ARE none.†
Chpt 3 *

principal = most important; or person that is most important

Principal mountains—I'm on the only one, but I don't think it's got any name.†
Chpt 3

Definitions:

(1) (principal)
most important; or person who is most important
The exact meaning of principal can depend upon its context. For example:
- "the principal idea" or "the principal performer" -- the most important
- "the principal of the school" -- the person in charge
- "a principal of a company" -- an owner or person with controlling authority
- "the principal in a transaction" (as contrasted to the agent) -- the person on whose behalf an agent acts
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

See a comprehensive dictionary for specialized senses in finance, architecture, law, chemistry, and music.