perilous (adj.)

c. 1300, from Old French perillos "perilous, dangerous" (Modern French périlleux) "dangerous, hazardous," 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." Related: Perilously; perilousness.