To wipe out half of all life in a population on any scale. Comes from the comic book villian Thanos who wanted to do this on a universal scale

To wipe out half of any population on any scale. Named after Thanos, a comic book villian in the Marvel Universe who wanted to wipe out half of all life to create balance

Wiping out half of a population(s) for any reason. Came for Thanos for wanting to greater balance in the universe

The killing of half of any specific or non-specific species

Thanocide is the act of killing half of any specific or non-specific species