What is Esnecy?

Legal Definition
Eldership. In the English law, this word signifies the right which the eldest coparcener of lands has to choose one of the parts of the estate after it has been divided.
-- Bouviers Law Dictionary
Legal Definition
Seniority; the condition or right of the eldest; the privilege of the eldest-born. Particularly used of the privilege of the eldest among coparceners to make a first choice of purparts upon a voluntary partition.
-- Black's Law Dictionary
Legal Definition
The share of the eldest.
-- Ballentine's Law Dictionary