One of the mix-ups your spell checker won´t notice:
principle:
1
a : a comprehensive and fundamental law, doctrine, or assumption
b (1) : a rule or code of conduct (2) : habitual devotion to right principles
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
b : an ingredient (as a chemical) that exhibits or imparts a characteristic quality
principal:
1
: a person who has controlling authority or is in a leading position: as
a : a chief or head man or woman
b : the chief executive officer of an educational institution
c : one who engages another to act as an agent subject to general control and instruction; specifically : the person from whom an agent’s authority derives
d : the chief or an actual participant in a crime
e : the person primarily or ultimately liable on a legal obligation
f : a leading performer : star
2
: a matter or thing of primary importance: as
a (1) : a capital sum earning interest, due as a debt, or used as a fund (2) : the corpus of an estate, portion, devise, or bequest
b : the construction that gives shape and strength to a roof and is usually one of several trusses; broadly : the most important member of a piece of framing