αὐτοβουλήτως
From LSJ
ἀναβάντα γὰρ εἰς τὴν ἀκρόπολιν, καὶ διὰ τὴν ὑπερβολὴν τῆς λύπης προσκόψαντα τῷ ζῆν, ἑαυτὸν κατακρημνίσαι → for he ascended the acropolis and then, because he was disgusted with life by reason of his excessive grief, cast himself down the height
English (LSJ)
A of one's own purpose, Hsch. s.v. ἐθελοντής.
