O / octāvusdĕcĭmus
adjective

octāvusdĕcĭmus

fem. octāvus-dĕcĭma · neut. octāvus-dĕcĭmum
the eighteenth •
the eighteenth: pars, Vitr. 3, 3: anno aetatis, Tac. A. 13, 6.