rhythmist

Etymology tree
Proto-Indo-European *ser-?
Proto-Indo-European *srew-
Proto-Indo-European *sru-dʰ-mo-s
Proto-Hellenic *hrutʰmós
Ancient Greek ῥῠθμός (rhŭthmós)bor.
Latin rhythmusder.
English rhythm
Proto-Indo-European *-id-
Proto-Indo-European *-yéti
Proto-Indo-European *-idyéti
Proto-Hellenic *-íďďō
Ancient Greek -ῐ́ζω (-ĭ́zō)
Proto-Hellenic *-tās
Ancient Greek -τής (-tḗs)
Ancient Greek -ῐστής (-ĭstḗs)bor.
Latin -istader.
Old French -istebor.
Middle English -ist
English -ist
English rhythmist
From rhythm + -ist.