octōgōnŏs — Lewis & Short
octōgōnŏs (octāgōnŏs), i, adj., = o)ktw/-gwni/a,
I eight-cornered, octagonal:
turris marmorea octogonos,Vitr. 1, 6, 4.— As subst.: octōgōnum, i, n., an octagon, Vitr. 1, 6, 4 al.