1. in anthropology, a major social division of many traditional societies consisting of a group of families that claim common ancestry. Clans often prohibit marriage between members and are often associated with reverence for a particular totem. See also descent group; phratry.

2. in Scotland and Ireland, a kinship group and former social unit based on traditional patterns of land tenure and the concept of loyalty to a clan chief. Clan members often took the name of the supposed clan founder prefaced by Mac (Scotland) or O’ (Ireland) but were not necessarily linked by common ancestry.