AC'TIAN, adjective Relating to Actium, a town and promontory of Epirus, as actian games, which were instituted by Augustus, to celebrate his navel victory over Anthony, near that town, Sep. 2, B.C. 31. They were celebrated every five years. Hence, actian years, reckoned from that era.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI