Of problematic origin. The name seems to have been first used in Spain and Portugal, and, according to tradition, was the name of the wife of St Paulinus of Nola, who spent most of his life in Spain; she was said to have originated (and to have derived her name) from the Greek island of Thēra. However, this story is neither factually nor etymologically confirmed.
English: habitational name of uncertain origin. The surname is common in London, and may be derived from Alsa (formerly Assey) in Stanstead Mountfitchet, Essex (recorded as Alsiesheye in 1268). Another possible source is Halsway in Somerset, named from Old English hals ‘neck’ + weg ‘way’, ‘road’.