Lewis & Short

mŏnaulos or mŏnaulus, i, m., = μόναυλος, a single flute, a flute with a single pipe (post-Aug.): fistulam et monaulum (invenit) Pan Mercurii, Plin. 7, 56, 57, § 204: saepe monaulon habet, Mart. 14, 64, 2; cf. monaules.