The Collaborative International Dictionary
Impacable
Impacable \Im*pa"ca*ble\, a. [L. pref. im- not + pacare to
quiet. See Pacate.]
Not to be appeased or quieted. [Obs.]
--Spenser. --
Im*pa"ca*bly, adv.
Wiktionary
impacable
a. (context obsolete English) Not to be appeased or quieted.