Math is even worse: group, ring, field, prime, associate, composite, unit, ideal, product, power, real, imaginary, fiber and on and on all have completely different meanings, which often have nothing in common with their ordinary meaning.
"ideal class group" sounds vaguely Marxist...
Every field of study has its own jargon, which simply has to be learned. Sometimes, as in the math examples, these are regular words. sometimes, like medicine or cladistics, they're made up for the occasion.
Gauss even borrowed Linnean taxonomic terms for the theory of quadratic forms: class, order, genus