If "most deathdealing" is the extreme end of a scale of lethality, then its antonyms would be words indicating the exact opposite. Some possible antonyms could include words like harmless, safe, benign, non-toxic, or non-lethal. These antonyms indicate the absence of danger, injury, or death. If we think of "most deathdealing" as a word that describes something that poses the greatest threat to life, then its antonyms refer to items or situations that are virtually without risk or harm. While there may indeed be many other antonyms for "most deathdealing," the key is that they convey the opposite meaning, and underscore the notion of safety and security.