We currently define prime numbers as those that have only 4 divisors: + or - itself, +1 and -1.
But when first thought out, most likely by Pythagoras, about 530 BC, the word prime was not related, but rather primary.
The idea of primary numbers, introduced by Pythagoras, continues today. For Pythagoras, there were primary numbers and secondary numbers. Simply put, primary or prime numbers are those that cannot be obtained by multiplying other numbers, and secondary numbers are those that can be generated by multiplying other numbers.
Over time, prime numbers were also called rectilinear, linear and eutimetric.