ˈdekyəmən adjective
Etymology: Latin decumanus, decimanus of the tenth, large, from decum us, 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