Aco, in the names of places once occupied by Algonquin bands, means, a limit, or as far as, and is intended to designate the boundary or reach of woods and waters.

Arm : Wan-na, or War-na : Aco, or Acol : Wor-nuck : Tarrang : - : Bar-gar : Co-pah : Yir-ra-wig.