The spelling of the word "rhythmeur" may seem unusual, but it is derived from the French word "rhythme" meaning rhythm. In IPA phonetic transcription, the pronunciation of "rhythmeur" is /rɪð.mjʊr/. It starts with the voiced alveolar fricative sound /ð/ and is followed by the combination of the two vowel sounds /ɪ/ and /ʊ/. The ending -eur is common in many French words indicating a practitioner of a particular profession or activity. Therefore, a "rhythmeur" is someone who works with rhythms.
An apparatus for securing rhythmic interruptions of the electric current in an x-ray machine.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.