dec·u·man \ˈdekyəmən\adjective Etymology: Latin decumanus, decimanus of the tenth, large, from decumus, decimus tenth (from decem ten) + -anus -an — more at ten 1.of a wave: extremely large : huge < that decuman wave that took us fore and aft — P.A.Motteux > 2.: of or relating to the tenth cohort — used especially of the chief gate of a Roman camp