Both Uses of

principal
in
Jane Eyre

From my seat I could look down on Thornfield: the grey and battlemented hall was the principal object in the vale below me; its woods and dark rookery rose against the west.†
p. 131.9 *

principal = most important; or person that is most important

Sometimes all, as with one consent, suspended their by-play to observe and listen to the principal actors: for, after all, Mr. Rochester and — because closely connected with him — Miss Ingram were the life and soul of the party.†
p. 219.2

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.