This etymology is one of two competing ones appealing to the same etymon θείνω, here taken in the passive meaning and with the restricted meaning "to cut, to pierce", not "to kill". The form θένω is a variant of θείνω. Neither combine with παρα- in Greek, but that was not an obstacle for Greek etymologists. In this explanation, the etymologist combines the etymon θείνω with a verb displaying the preverb παρα- (παρεῖναι), so as to provide a source for the first syllable of παρθένος.