All 5 Uses

principle
in
The Hunt for Red October
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It was a new principle, something unexpected that cropped up.†
Chpt 4. *

principle = basic rule or belief
Remember that they had already stumbled across one new principle, that back-pressure thing.†
Chpt 4.
It is a principle of diplomacy," Pelt observed, "that one must know something of the truth in order to lie convincingly."†
Chpt 8.
What they got was a new principle of hydrodynamics.†
Chpt 8.
Everyone knew the principles on which SAPS operated, but there were probably not fifty men in the country who could really explain the nuts and bolts details.†
Chpt 12.

principles = basic rules or beliefs

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.