Rosmerta
Gallic goddess of prosperity, whose name means "great provider." According to the Romans, she was the consort of "Mercury," who here may be Lugus (the Gallic Lugh), or the god Esus (both of whom may be the same god). All that is known of her cult are the remains of altars dedicated to her, with her image and that of "Mercury" carved into said altars. She is also depicted with a cornucopia and a cadeucus, appropriately. Her cult was centered in southern Gaul, and along the Rhone and Rhine, as well as South-west Britain.
Her connection to "Mercury," if we equate Mercury with Lugh, would possibly make her equivalent to the Irish goddess Tailtiu. I do not know of a Welsh equivalent.