What is "tongoenabiagus"

Tongoenabiagus was the god of the Fonte do Ídolo ( Portuguese for Fountain of the Idol), a 1st-century shrine in Braga (the Roman Bracara Augusta) with an inscribed fountain dedicated both to Tongoenabiagus and the goddess Nabia. His name may derive from the Celtic root *tenge(o)- (Old Irish tongu "I swear") and so he may have been associated with the swearing of oaths.