IPA: //ˈklævɪərɪst//
KK: /ˈklævɪərɪst/
A person who plays a keyboard instrument, such as a piano or organ.
The clavierist performed beautifully at the concert last night.
Clavierist is formed from "clavier" (from French, meaning keyboard or piano) and "-ist" (meaning one who practices or is concerned with). A clavierist is someone who plays the keyboard or piano.
Think of a 'clavier' as a keyboard instrument and '-ist' as someone who plays it — that's why a clavierist is a person who plays the keyboard.