Lewis & Short

hēmĕrŏdrŏmus, i, m., = ἡμεροδρόμος (who runs the day through), a courier (pure Lat. cursor, Plin. 2, 71, 73, § 181): nisi speculator (hemerodromos vocant Graeci) ingens die uno cursu emetiens spatium, etc., Liv. 31, 24, 4.
In plur.: hemerodromœ, Nep. Milt. 4, 3.