fraught with danger; "dangerous waters"; "a parlous journey on stormy seas"; "a perilous voyage across the Atlantic in a small boat"; "the precarious life of an undersea diver"; "dangerous surgery followed by a touch-and-go recovery"
Something that is perilous is very dangerous. a perilous journey across the war-zone The road grew even steeper and more perilous. + perilously peri·lous·ly The track snaked perilously upwards. very dangerous