Lewis & Short

antispastus, i, m., = ἀντίσπαστος (reversed), in metre (sc. pes), an antispast, a foot in verse, ⏑––⏑, i. e. the choriambus reversed, e. g. Mĕdūllīnă, Diom. p. 478 P.; hence: antispasticum metrum, verse consisting of antispasts, id. p. 505 P.