rhythmist
/ˈrɪðmɪst/noun
A person who uses or is expert in rhythm. Formerly also: †= rhymist. Now also: a member of a rhythm section.
Origin
Late 18th century; earliest use found in William Enfield (1741–1797), Unitarian minister. From rhythm + -ist. With use in sense ‘rhymist’ compare rhythm and discussion at that entry.