Gaulish: Bright, Shining
Also: Bile, Beli, Beli Mawr, Belinus, possibly Balor, and the Arthurian Pellinor, Pelles (though Pelles may also be Pwyll).
The Gaulish (continental Celtic) god of light, specifically the sun, it is thought, as Lugos/Lugh/Lleu is also a god of light, though not necessarily of the sun, as the sun in insular mythology is often called Grainne, a feminine name, and thus the sun is conjectured to be a goddess. Lugos is equated instead with Mercury/Hermes.
All that is known of Belenos is that he is the patron of Beltain (the First of May), and the god refered to by Julius Caesar as Apollo. However, monuments attest to Maponos/Mabon ap Modron as being Apollo; Maponos is also a sun deity, and these may be forms of the same god.
He is also equated in some monuments with Cernunnos; see Beli Mawr