Merriam-Webster Collegiate Dictionary - principle

 noun  Etymology: Middle English, from Middle French principe, ~, from Old French, from Latin principium beginning, from princip-, princeps initiator — more at prince  Date: 14th century  1.  a. a comprehensive and fundamental law, doctrine, or assumption  b.  (1) a rule or code of conduct  (2) habitual devotion to right ~s a man of ~  c. the laws or facts of nature underlying the working of an artificial device  2. a primary source ; origin  3.  a. an underlying faculty or endowment such ~s of human nature as greed and curiosity  b. an ingredient (as a chemical) that exhibits or imparts a characteristic quality  4. capitalized, Christian Science a divine ~ ; god Usage:  Although nearly every handbook and many dictionaries warn against confusing ~ and principal, many people still do. Principle is only a noun; principal is both adjective and noun. If you are unsure which noun you want, read the definitions in this dictionary.