WordNet sense 1 (dangerously unstable and unpredictable):

treacherous

WordNet sense 2 (fraught with danger):

parlous, perilous, precarious

WordNet sense 3 (involving risk or danger):

hazardous, risky

WordNet sense 4 (of uncertain outcome; especially fraught with risk):

chancy

WordNet sense 5 (moving at very high speed):

breakneck

WordNet sense 6 (involving or causing danger or risk; liable to hurt or harm):

unsafe

WordNet sense 7 (causing fear or anxiety by threatening great harm):

grievous, life-threatening, serious, severe, grave

WordNet sense 8 (being in or verging on a state of crisis or emergency):

critical