perilous (adj.) Look up perilous at Dictionary.com
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.