corycus
From LSJ
cōrycus: (cōrĭ-), i, m., = κώρυκος,
I a leathern sack filled with sand, flour, etc., by means of which the athletae exercised in the palæstra; only fig.: corycus laterum et vocis meae Bestia, Cic. Phil. 13, 12, 26 B. and K., Halm; cf. Klotz and Orell. ad loc.