fatal
1 deadly, destructive, final, incurable, killing, lethal, malignant, mortal, pernicious, terminal
2 baleful, baneful, calamitous, catastrophic, disastrous, lethal, ruinous
3 critical, crucial, decisive, destined, determining, doomed, fateful, final, foreordained, inevitable, predestined
1 & 2 beneficial, benign, harmless, inconsequential, innocuous, inoffensive, minor, non-lethal, non-toxic, salutary, vitalizing, wholesome