The Gaulish theonymAlaunos stems from a Proto-Celtic form reconstructed as *Alamnos. The etymology remains uncertain. It has been traditionally derived from the root *al- ('feed, raise, nurture'), and compared with the Latin alumnus ('nursling') and with names of rivers such as Almus in Moesia, Yealm (*Almii) in England, or Alme in Westphalia. *Alamnos could thus be translated as 'the Nourishing One'.[3][4]
A Gallic tribe named Alauni (Αλαυνοί) is also attested in Noricum, and linguist Xavier Delamarre has argued that the root alǝ-, meaning 'to wander', "would suit river names as much as ethnic ones". In this view, *Alamnos may be compared with the Celtic stem *alamo- ('herd'; cf. Old Irish alam, Welsh alaf), and the ethnonymAlauni rendered as the 'errants' or the 'nomads', contrasting with the name of the Anauni ('the Staying Ones').[3]
^Matasović 2009, p. 30: "The Gaul. toponym Alaunos and hydronym Alauna are usually derived from the same root, but like most etymologies of toponomastic elements, this is also uncertain."
Bibliography
Delamarre, Xavier (2003). Dictionnaire de la langue gauloise: Une approche linguistique du vieux-celtique continental. Errance. ISBN9782877723695.