The Collaborative International Dictionary of English v.0.48:

Routously \Rout"ous*ly\, adv. (Law)
   With that violation of law called a rout. See 5th Rout, 4.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

ROUTOUSLY, pleadings. A technical word properly used in indictments for a
rout as descriptive of the offence. 2 Salk. 593.