principal
The original amount of money you lend or invest before any interest or growth is added. It is the starting number everything else is calculated from.
Where it is explained in full
Bonds and Treasuries: lending money, with a price that moves. A bond is a loan you make. The interest is fixed, the price is not, and the relationship between the two confuses nearly everyone the first time.
A definition says what a thing is; it never says whether it fits you. The guides explain how it works and name the professional who confirms it for a particular person. The No Advice Disclosure.
Ask about principal
A model reads this page and answers from it. It will say when the answer is not on the page. Education, not personalized advice.