Both Uses

principal
in
Bridge to Terabithia
(Auto-generated)

"Blowing in the Wind," and because Mr. Turner, the principal, insisted, "God Bless America."†
p. 18.9 *

principal = most important; or person that is most important
There was a moment of silence while they both considered what Janice Avery might do to anyone who reported her to the principal.†
p. 76.7

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