Interesting discussion, thus so far. I found these 2 definitions, both from Webster's Dictionary (one from 1913 and, the other is from Webster's website).


Webster's Revised Unabridged Dictionary (1913):
Clan \Clan\, n. [Gael. clann offspring, descendants; akin to Ir. clann, cland, offspring, tribe, family; perh. from L. plania scion, slip, cutting. Cf. Plant, n.]

1. A tribe or collection of families, united under a chieftain, regarded as having the same common ancestor, and bearing the same surname; as, the clan of Macdonald. ``I have marshaled my clan.'' --Campbell.

2. A clique; a sect, society, or body of persons; esp., a body of persons united by some common interest or pursuit; -- sometimes used contemptuously.

Partidge and the rest of his clan may hoot me. --Smolett.

The whole clan of the enlightened among us. --Burke.


Merriam-Webtser Online:
Clan

Pronunciation: \ˈklan\

Function: noun

Etymology: Middle English, from Scottish Gaelic clann offspring, clan, from Old Irish land plant, offspring, from Latin planta plant

Date: 15th century

1 a: a Celtic group especially in the Scottish Highlands comprising a number of households whose heads claim descent from a common ancestor b: a group of people tracing descent from a common ancestor : family

2: a group united by a common interest or common characteristics