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
Tom took his whipping and went back to his seat not at all broken-hearted, for he thought it was possible that he had unknowingly upset the ink on the spelling-book himself, in some skylarking bout—he had denied it for form's sake and because it was custom, and had stuck to the denial from principle.
Chapter 20 (64% in)
There are no more uses of "principle" in The Adventures of Tom Sawyer.