1A person who belongs to a group (without implication of greater than usual involvement or commitment).
2A person who actively participates in the activities of a group. Also (chiefly Marketing): a person who derives happiness or satisfaction from being part of a group; a person who strongly identifies with a group, a conformist.
3Also with capital initial. In some current and former British colonies and overseas territories: an immigrant who is a long-term resident; especially one who has acquired the legal right to live and work indefinitely in that place, or who has been granted citizenship thereof.
4Caribbean A native of a particular island; a non-immigrant.
Late 16th century (in an earlier sense). From belong + -er.