Definitions for natural law
Random House Webster's College Dictionary
a principle or body of laws considered as derived from nature, right reason, or religion and as ethically binding in human society.
Origin of natural law:
law, natural law(noun)
a rule or body of rules of conduct inherent in human nature and essential to or binding upon human society
An ethical theory that posits the existence of a law whose content is set by nature and that therefore has validity everywhere.