Synonyms for Principle (same or very similar meaning)
WordNet sense 1 (rule of personal conduct):
preceptWordNet sense 2 (a basic generalization that is accepted as true and that can be used as a basis for reasoning or conduct):
ruleWordNet sense 3 ((law) an explanation of the fundamental reasons (especially an explanation of the working of some device in terms of laws of nature)):
rationaleFrom the ODE community, based on WordNetadd/edit