principal

(1) The total amount of money being borrowed or lent. (2) The party affected by agent decisions in a principal-agent relationship.

Amount of debt, not including interest. The face value of a note, mortgage, etc.
See PRINCIPAL MERIDIAN 

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The face amount of a bond.
The amount of money (exclusive of interest) paid or received when a bond is traded.

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The original amount or face value of a investment, typically bonds and CDs, on which interest is owned or earned. Interest is paid based on a percent of the principal (a stated interest or coupon rate). At maturity, the entire principal is returned to investor; however its purchasing value may be diminished by inflation.

The basic element of the loan as distinguished from interest and mortgage insurance premium. In other words, principal is the amount upon which interest is paid.