Canonum De Ius Rex
Canons of Sovereign Law
II. Sovereign
2.3 Tará Law Form
Article 35 - Fine
Canon 5631 (link)
When an prísonóir (honor price) was to be paigh (origin of paid) under Celtic law, then such payments were usually made to the Fine. Hence, the ancient maxim of law “pay the fine” which has continued in words only.