רְתֹ֧ם הַמֶּרְכָּבָ֛ה לָרֶ֖כֶשׁ יוֹשֶׁ֣בֶת לָכִ֑ישׁ רֵאשִׁ֨ית חַטָּ֥את הִיא֙ לְבַת־צִיּ֔וֹן כִּי־בָ֥ךְ נִמְצְא֖וּ פִּשְׁעֵ֥י יִשְׂרָאֵֽל׃
Rashi on Micah
Hitch the chariot to the swift steeds Heb. רְתֹם הַמֶּרְכָּבָה לַרֶכֶשׁ. Hitch the chariot to the רֶכֶשׁ, which is swift to run, and you shall escape. The word רֶכֶשׁ is explained by Dunash (Teshuvoth Dunash p. 69) as an Arabic word.