ῥοϊσμός
From LSJ
εἰ δὲ τύχῃ τις ἔρδων, μελίφρον' αἰτίαν ῥοαῖσι Μοισᾶν ἐνέβαλε → if someone is successful in his deeds, he casts a cause for sweet thoughts into the streams of the Muses
English (LSJ)
ὁ, (ῥοΐζω) A = ὁ τῶν ἵππων ῥισμός (sic), Hsch.
Greek (Liddell-Scott)
ῥοϊσμός: ὁ, (ῥοΐζω) κολύμβημα, ἐπὶ ἵππων, «ροϊσμός· ὁ τῶν ἵππων» Ἡσύχ.