Dec"u*man (?), a. [L. decumanus of the tenth, and by metonymy, large, fr. decem ten.]
Large; chief; -- applied to an extraordinary billow, supposed by some to be every tenth in order. [R.] Also used substantively.
"Such
decuman billows."
Gauden. "The baffled
decuman."
Lowell.
© Webster 1913.