obsolete A criminal who boards and plunders waterborne ships (i.e., arks), usually with the aid of one or more of its crew, sometimes resulting in the murder of its passengers. Aye, but the waters are treacherous these days, and the ark ruffians make even the most placid trip a journey to be wary of.
See also: ark
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.