Ismene was the daughter of Oedipus and Jocasta, and the sister of Antigone. Thomas Keightley suggests that she may have been invented for sake of uniformity, in order to balance Antigone. There would then have been two brothers (Eteocles and Polynices) and two sisters. However that may be, we can contrive an origin for her to mean 'revealing strength', from is, 'strength', 'force' and menyo, 'to disclose', 'reveal'. Those of the 'ritual and historical' school, however, will probably derive the second half of the name from mené, 'moon'.