What is Pur?

Legal Definition
A corruption of the French word par, by or for. It is frequently used in old French law phrases; as, pur autre vie. It is also used in the composition of words, as purparty, purlieu, purview.
-- Bouviers Law Dictionary
Legal Definition
L. Fr. By or for. Used both as a separable particle, and in the composition of such words as "purparty," "purlieu."
See also
-- Black's Law Dictionary
Legal Definition
For.
-- Ballentine's Law Dictionary