Cathussach mac Eterscélai (died circa 769) was a king of Munster from the Eóganacht Áine branch of the Eóganachta.
According to the Laud Synchronisms, he succeeded Cathal mac Finguine (died 742) of the Eóganacht Glendamnach branch in 742 and reigned for 27 years.
[2] Cathussach's branch of the family bordered on Cliú, but it is not known if the battle was fought by him or by the minor tribes of this region resisting Uí Fidgenti subjugation.
[3] Local power politics here were caused by the vacuum left by the decline of the Ui Fiachrach Aidhne of Connacht.
In 747 the Battle of Carn Ailche (possibly Carnelly, County Clare) is recorded as having occurred amongst the men of Munster, in other words, a civil war.