From BiblePortal Wikipedia

Webster's Dictionary [1]

(1): (n.) 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.

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

The Nuttall Encyclopedia [2]

A tribe of blood relations descended from a common ancestor, ranged under a chief in direct descent from him, and having a common surname, as in the Highlands of Scotland; at bottom a military organisation for defensive and predatory purposes.