Both Uses

principle
in
She Said Yes
(Edited)

She had principles and morals, and she was not ashamed of them, even though it must have taken all the courage she could muster to hold fast.
p. 132.1 *

principles = basic rules or beliefs
Rachel Scott, another classmate, seems to have been targeted for her principles too—at least that's what her friend Andrea says: Rachel stood up for what she thought and paid for it.
p. 132.8

Definitions:

(1) (principle)
a basic rule or belief
The exact meaning of principle can depend upon its context. For example:
- "our guiding principles" -- basic moral beliefs that guide decisions and behavior
- "electromagnetic principles" -- rules describing how the world works
- "She lacks principles." -- lacks moral guidelines
- "We agree in principle." -- about important basic beliefs
(2) (meaning too rare to warrant focus)
See a comprehensive dictionary for more specialized senses including one in chemistry.