The Collaborative International Dictionary of English v.0.48:
never-say-die \never-say-die\ adj. Incapable of being subdued. Syn: indomitable, unsubduable. [WordNet 1.5]WordNet (r) 3.0 (2006):
never-say-die adj 1: impossible to subdue [syn: indomitable, never-say- die, unsubduable]