gens

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A patrilineal clan of ancient Rome composed of several families of the same name claiming a common ancestor and belonging to a common religious cult.
• noun Anthropology An exogamous patrilineal clan.

from The Century Dictionary.

• noun In ancient Rome, a clan or house embracing several families claiming descent from a common ancestor, united by a common name and by certain religious rites and legal privileges and obligations, but not necessarily by consanguinity: as, the Fabian gens, all bearing the name Fabius; the Julian gens, all named Julius; the Cornelian gens, etc.
• noun In historical and ethnological use, a tribe or clan; any community of persons in a primitive state of society constituting a distinct or independent branch of a general aggregate or race.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Rom. Hist.) A clan or family connection, embracing several families of the same stock, who had a common name and certain common religious rites; a subdivision of the Roman curia or tribe.
• noun (Ethnol.) A minor subdivision of a tribe, among American aborigines. It includes those who have a common descent, and bear the same totem.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A legally defined unit of Roman society closest in meaning to and translated by English clan, but not identical to it. The gens was a collection of families whose members were related by birth, marriage or adoption. All the families were considered to have descended from a common clan ancestor although in cases where the time from the ancestor to the contemporary time was great the kinship was more remote than is meant by the English term "related." In such cases the legal definition still prevailed.
• noun anthropology a tribal subgroup whose members are characterized by having the same descent, usually along the male line
• abbreviation generations

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun family based on male descent