Synonym of central city (“the main city of a metropolitan area; particularly one containing multiple cities”). / Used other than figuratively or idiomatically: see principal, city.

(algebra) An integral domain in which every ideal is a principal ideal.

(physics) The quantum number (of an atomic orbital) that specifies the energy of an electron in an atom and, hence, which shell it occupies

(algebra, ring theory) A commutative ring in which every ideal is a principal ideal.

plural of principal ideal ring

plural of principal quantum number

plural of principal ideal domain

(mathematics) The positive square root of a number; the positive number which, when squared, yields another number

plural of principal-agent problem

The problem that a person or entity serving as an agent for another, and able to make decisions on the other's behalf, may be motivated instead to make decisions that benefit themselves.