means First in rank, quality, or importance — or, in math, a whole number divisible only by 1 and itself.

from From Latin primus, "first," the same root that fronts primary, premier, and prince. It entered English through the Church's prima hora — the "first hour" of daily prayers, sung at dawn. Over centuries that sense of firstness spread everywhere: prime cuts, prime suspects, prime ministers, and the mathematician's prime number, first and indivisible.