Possible Clues:

• Property of Electra's instruction to Orestes?
• Commit matricide for the sake of her estate (6)
• Kill the old girl for her place
• Sphere in which to commit matricide
• Perhaps commit matricide around 18 down
• Scope of knowledge - owned land
• Country's premier following dupe
• Territory governed by the same chief
• Commit matricide in the field
• A district sphere of influence