Thanks Jan for your answer! I am glad that I asked this question.
Is an accurate understanding of these words/labels important? I think so, because it helps the brain to internalize the quality of sound.
What is a pure sound? (I guess a not distorted sound)
What is a rich sound? (I guess a brassy sound with lots of overtones, opposite of mellow)
What is a rich, pure and centered sound?
Are there other labels that describe the quality of sound?