IPA: /ˈdɛθliːər/
KK: /ˈdɛθliːər/
More likely to cause death or be fatal; more deadly.
The new virus is considered deathlier than previous strains.
Deathlier → It is formed from "death" (from Old English "deað", meaning the end of life) and "-lier" (a comparative suffix indicating more). The word "deathlier" means more deadly or causing more death than something else.
Think of 'death' as the end of life, and the '-lier' suffix means more. So, deathlier refers to something that causes more death.