English definition of “principle”
MORAL RULE [C, U] › a rule or belief which influences your behaviour and which is based on what you think is right: He must be punished - it's a matter of principle.
BASIC IDEA [C] › a basic idea or rule which explains how something happens or works: The organization works on the principle that all members have the same rights.
in principle › If you agree with something in principle, you agree with the idea or plan although you do not know the details or you do not know if it will be possible: They have approved the changes in principle.
on principle › If you refuse to do something on principle, you refuse to do it because you think it is morally wrong: She doesn't wear fur on principle.