Entry 1 sense Webster, 1913 Actium · IPA /ˈæk.ti.əm/ 01 n. naval battle where Antony and Cleopatra were defeated by Octavian's fleet under Agrippa in 31 BC. 1. naval battle where Antony and Cleopatra were defeated by Octavian's fleet under Agrippa in 31 BC.