perilous (adj.)

c. 1300, "full of danger; risky; involving exposure to death, destruction or injury," also "spiritually dangerous," from Old French perillos "perilous, dangerous" (Modern French périlleux), from Latin periculosus "dangerous, hazardous," from periculum "a danger, attempt, risk," with instrumentive suffix -culum and first element from PIE *peri-tlo-, suffixed form of root *per- (3) "to try, risk." In Arthurian romances, the sege perilous (c. 1400) was the seat reserved for the knight who should achieve the quest of the Grail. Related: Perilously; perilousness.