The Collaborative International Dictionary
Potestative
Potestative \Po*tes"ta*tive\, a. [L. potestativus, fr. potestas
power: cf. F. potestatif. See Potent.]
Authoritative. [Obs.]
--Bp. Pearson.
Wiktionary
potestative
a. 1 (context obsolete English) authoritative 2 (context legal English) of a condition in a legal contract: being completely controlled by exactly one of the party to the contract