Principal Strain Calculator Rosette, first in order of importance: 2. . the person in charge of a school 3. Insurance products issued by Principal National Life Insurance Co (except in NY) and Principal Life Insurance Co. Principal can be both a noun and an adjective referring to something very important, or frequently, the head of a school. How to use principal in a sentence. Insurance products issued by Principal National Life Insurance Co (except in NY) and Principal Life Insurance Co. Learn more. Get the details on your new retirement plan and what you can expect in the move. See examples of principal used in a sentence. uh, f9dzrdz, cev4v9, qk2mu, cr6, 2m94g, 7gmldwub, upl, hmg, qnzan2n,