TIL: OHG rīm didn't mean Reim/rhyme but number, series; the original meaning that's still the case in Welsh rhif. the same is true of ON rim vs. modern Scandinavian, and Old Frisian rīm vs. modern.
also ᾰ̓ρῐθμός is a cognate—I'm so used to stuff like this coming from Arabica that I had assumed it was from al-something.