The one [doing something] with his own hand, or the one who kills himself. Hence in Isocrates perpetrator.[1]
Lysias applies it in a special sense to the 30, even though they had their murders committed by others. For 'the actual perpetrator' always denotes the one who does it with his own hand.[2]
Also [sc attested is the related participle] au)qenth/santa, [meaning him] having gained control. "It would do him no good to have gained control of the ones in uniform to keep them together."[3]
"Mithridates had given commands that the Romans be killed and had sent letters bearing the royal seal to the cities instructing that the messages be read and carried out on the same day so that certain people would not be forewarned and take precautions, for he had ordered them to kill each and every Roman they could find. And to increase the multitude of corpses he proposed rewards not only for those of them who were to be the perpetrators, but also to the people among whom they happened to die, and specified a serious penalty for those who spared any of them."[4]
*au)qenths is derived as follows. There is a verb fw=, [meaning] 'I slaughter',[5] out of which fo/nos ["slaughter"] also [comes]. Out of this, alteration produces fe/nw with the epsilon; by aphaeresis of the phi, e)/nw. Out of this [comes] e)/nths and with the pronoun au)to/ ['self', 'very'], au)toe/nths. And since smooths leads smooths and roughs roughs, by change of the tau into theta, au)qe/nths, 'the one who does it with his own hand'.[6] But habit has taken over and uses the word as a synonym for 'master' -- which is a soloecism.