All 6 Uses of

principal
in
Frankenstein - 1831 version

We resided principally in the latter, and the lives of my parents were passed in considerable seclusion.†
p. 38.9 *

principally = primarily or most importantly

The next morning I delivered my letters of introduction and paid a visit to some of the principal professors.†
p. 47.1

principal = most important; or person that is most important

I replied carelessly, and partly in contempt, mentioned the names of my alchemists as the principal authors I had studied.†
p. 47.3

Such were my reflections during the first two or three days of my residence at Ingolstadt, which were chiefly spent in becoming acquainted with the localities and the principal residents in my new abode.†
p. 48.5

Clerval desired the intercourse of the men of genius and talent who flourished at this time, but this was with me a secondary object; I was principally occupied with the means of obtaining the information necessary for the completion of my promise and quickly availed myself of the letters of introduction that I had brought with me, addressed to the most distinguished natural philosophers.†
p. 163.2

principally = primarily or most importantly

Frankenstein discovered that I made notes concerning his history; he asked to see them and then himself corrected and augmented them in many places, but principally in giving the life and spirit to the conversations he held with his enemy.†
p. 213.4

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.