Principle
A principle is a comprehensive and fundamental law, doctrine, or assumption, and whose idea is a central one in Western thought. For example the action of "change" is said to be based on five principles.
Commonly used synonyms for principle are (originative) "source" or "beginning".
For example, in some senses a "nature" is the source of a thing's action, and an "essence" is the source of a thing's being.
A "cause" is a kind of principle, but the meaning of principle can be broader than "cause" in at least two ways. Firstly, a principle can be a "deprivation" in the sense of the absence of a thing understood to be present by nature. An example could be the absence of a woman's eye, of which could be spoken as a principle of certain actions.
Secondly, in Christian theology, the Son of God and Holy Spirit were not created but are said to have God the Father as their "source" or principle.
An element or component or part is a kind of principle, which can always be a material cause; sometimes a final cause or end or an efficient cause or means; but never a formal cause (because the form into which a thing is caused to be must be a unity unless understood to be divisible, in which case the form is not the essential form of the thing, and the dividends are able to be considered separately with their own set of other causes.
So there is a kind of hierarchy of the senses of principle, cause and element.
Principles can be divided along three primary dimensions: principles of reality, moral principles and logical principles.