/dek"yoo meuhn/ , adj.
1. large or immense, as a wave.
2. (in ancient Rome) of or pertaining to the tenth cohort of a legion.
n.
3. Also called decuman gate . (in ancient Rome) the main gate of a military camp, facing away from the enemy and near which the tenth cohort of the legion was usually stationed.
[ 1650-60; decumanus, decimanus of the tenth, large, equiv. to decim ( us ) tenth (see DECIMATE) + -anus -AN ]