The Collaborative International Dictionary of English v.0.48:

Algonquian \Al*gon"qui*an\, a.
   Pertaining to or designating the most extensive of the
   linguistic families of North American Indians, their
   territory formerly including practically all of Canada east
   of the 115th meridian and south of Hudson's Bay and the part
   of the United States east of the Mississippi and north of
   Tennessee and Virginia, with the exception of the territory
   occupied by the northern Iroquoian tribes. There are nearly
   100,000 Indians of the Algonquian tribes, of which the
   strongest are the Ojibwas (Chippewas), Ottawas, Crees,
   Algonquins, Micmacs, and Blackfeet. -- n. An Algonquian
   Indian.
   [Webster 1913 Suppl.] Algonquin

WordNet (r) 3.0 (2006):

Algonquian
    adj 1: of or relating to an Algonquian tribe or its people or
           language [syn: Algonquian, Algonkian, Algonquin]
    n 1: a member of any of the North American Indian groups
         speaking an Algonquian language and originally living in
         the subarctic regions of eastern Canada; many Algonquian
         tribes migrated south into the woodlands from the
         Mississippi River to the Atlantic coast [syn: Algonquian,
         Algonquin]
    2: family of North American Indian languages spoken from
       Labrador to South Carolina and west to the Great Plains [syn:
       Algonquian, Algonquin, Algonquian language]