IPA: /ˈæltoʊɪst/
KK: /ˈæltoʊɪst/
A musician who plays an alto instrument, especially the alto saxophone.
The altoist played a beautiful solo during the concert.
Altoist is formed from "alto" (from Italian "alto", meaning high or elevated) and "-ist" (meaning one who practices or is concerned with). An altoist is a person who sings or plays in the alto range, which is a high vocal range.
Think of 'alto' meaning high, and '-ist' indicating a person. An altoist is someone who performs in the high vocal range.