​ASTRAGAL (from the Gr. ἀστράγαλος, the ankle-joint), an architectural term for a convex moulding. This term is generally applied to small mouldings, “torus” (q.v.) to large ones of the same form. The Lesbian astragal referred to by Vitruvius, bk. iv. ch. vi., was in all probability an astragal carved with a bead and reel enrichment.