UNEXTIN'GUISHABLE, adjective 1. That cannot be extinguished; unquenchable; as unextinguishable fire. 2. That cannot be annihilated or repressed; as an unextinguishable thirst for knowledge. [But inextinguishable is more generally used.]
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI