1. Involving exposure to very great danger; full of or involving danger: "Fears of a system-wide banking failure have receded, but we are still in perilous waters."
2. Involving or full of grave risk or peril; hazardous; fraught with danger.
3. Etymology: in use since about 1290, from Old French perillous, (French périlleux), "dangerous, hazardous"; which came from Latin periculosus, from periculum, "dangerous".