Cermand Cestach was the name of a gold-covered pagan idol which stood in Clogher Cathedral, County Tyrone, Ireland until medieval times. Alternative spellings are "Cermand Celstach", "Cermaed Celsetacht", "Kermand Kelstach", "Kerman Kelstach" and the Giant Ermand Kelstach.
Oracle interpretation
It seems Cermand Cestach was the name of the Oracle of Clogher, a stone which spoke through the Druids, somewhat like the Oracle of Delphi. The website http://www.irishmegaliths.org.uk states:
The reason the Lía Fáil was called "The Stone of Destiny" was because it told your destiny. All three stones were modelled on the Navel Stone or Omphalos of Delphi at the Delphi Oracle in Greece and closely resemble it.
There is another oracle mentioned in The Metrical Dindshenchas, poem 102 on Druim Tairleime: