Of Celtic origin and uncertain derivation (possibly a diminutive of a word meaning ‘rock’). It was introduced into England by Breton followers of William the Conqueror, most notably Alan, Earl of Brittany, who was rewarded for his services with vast estates in the newly conquered kingdom. In Britain the variants Allan and Allen are considerably less frequent, and generally represent transferred uses of surname forms, whereas in America all three forms of the name are approximately equally common. See also Alun.
English, Scottish, and northern Irish: distinguishing name (Middle English yunge, yonge ‘young’), for the younger of two bearers of the same personal name, usually distinguishing a younger brother or a son. In Middle English this name is often found with the Anglo-Norman French definite article, for example Robert le Yunge.