Grannus
In the Celtic polytheism of classical antiquity, Grannus (also Granus, Mogounus, and Amarcolitanus) was a deity associated with spas, healing thermal and mineral springs, and the sun. He was regularly identified with Apollo as Apollo Grannus. He was frequently worshipped in conjunction with Sirona, and sometimes with Mars and other deities.
In the early twentieth century, the name was connected with the Irish grian, ‘sun’. Along these lines, the god was often linked to the Deò-ghrèine and the character Mac Gréine of Irish mythology. However, the Irish grian, ‘sun’ is thought to be derived from Proto-Celtic *greinā ‘sun’ and the Proto-Celtic *greinā is unlikely to have developed into Grannos in Gaulish and other Continental Celtic languages. Derivation from a Proto-Celtic root *granno- ‘beard’ (cf. Middle Welsh grann ‘chin; beard, hairs’ and Old Irish grend ‘beard, hairs’) has enjoyed some scholarly support, from which Jürgen Zeidler dissents, proposing a different root *granno- with "probable reference to the sun's heat and healing properties".Ranko Matasović, in his Etymological Dictionary of Proto-Celtic, has tentatively proposed that the root of this theonym comes from Proto-Celtic *gwrenso-, which means "heat"; however, Proto-Celtic initial gw- yields b- in Gaulish (cf. the name Brennus).
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