ripienist
/ˌrɪpɪˈeɪnɪst/ /rɪpɪˈɛnɪst/Music
noun
In baroque music: an instrumental (or vocal) performer who only plays (or sings) to reinforce the full ensemble, as opposed to one of the principal performers (concertists).
Origin
Early 19th century; earliest use found in New Monthly Magazine. From ripieno + -ist, after German Ripienist.