allen

The surname Allen is a patronymic form, meaning "son of Alan." The given name Alan entered England following the Norman Conquest of 1066, brought by the Breton followers of William the Conqueror. The name's ultimate origins are debated but are often traced to Celtic roots, possibly related to the Proto-Celtic alanno-, meaning "rock" or "harmony." Over centuries, the name became widely established in the British Isles, evolving from a first name into a common hereditary surname, losing its transparent internal structure in the process.

This is a simplex proper noun. As a surname, it is a fused, unsegmentable unit in modern English. Its historical origin is from the given name Alan, which is of uncertain etymology, possibly from a Celtic word meaning "rock" or "harmony," or from a tribe mentioned by the Roman poet Juvenal.