The Proto-Indo-European word *nek̂s
Word *nek̂s
Meaning dead person, death
Synonyms *mr̥tís, *mr̥tóm, *móros

Comments
Skr. naśyati, Av. nasyeiti, Gk. nekros, Lith. našlys, Lat. nex, Toch. näk/näk, Ir. éc/eug, Welsh angeu, ON Naglfar

Other words that might be of interest
*hₐóyus ‘vital force, life, age of vigour’, *wel- ‘die’, *mr̥tós ‘dead, mortal’, *mórtos ‘person, mortal, man’