implacable
im.pla.ca.ble \(')im-'plak-*-b*l, -'pla--k*-\ \-ble-\ aj [MF or L; MF, fr.
L implacabilis, fr. in- + placabilis placab]le 1: not placable : not
capable of being appeased, pacified, or mitigated 2: UNALTERABLE -
im.pla.ca.ble.ness n
Webster's English Dictionary