"COMPLEMENT" and "COMPLIMENT"
"Complement" means to complete or enhance. "Compliment" means to praise or express admiration. Ex.: The sauce complements the dish perfectly. She complimented him on his presentation.
"PRINCIPAL" and "PRINCIPLE"
"Principal" refers to a person in a position of authority or the primary part of something. "Principle" means a fundamental rule or belief. Ex.: The school principal addressed the students. The principal reason for our success is teamwork. Honesty is an important principle to uphold.