Perilous means full of grave danger. A perilous journey, perilously close, a perilous state.
It is formal and slightly literary — perilous belongs to journeys, crossings and situations described from a distance, where dangerous does the everyday work. Perilously is used as an intensifier before close and near. Note peril, which is the noun; at your peril, meaning at your own risk; and that peril comes from the Latin for a trial or attempt, the same root as experiment.
1adjectiveperilousFull of grave danger.
“The climbers made a perilous journey across the ice in the dark.”
synonyms: hazardous, treacherous
perilous is a quality of danger.
Also accepted in games: dangerous, hazardous
Latin periculosus comes from periculum, a trial or danger, from a root meaning to try. Experiment, expert and empirical come from the same trying.
Proto-Indo-European
*per-
Latin
perīculōsus
Old French
perilleus
Middle English
perilous
English, today
perilous
From Middle English perilous, from Old French perilleus, equivalent to peril + -ous, from the noun peril, or from Latin perīculōsus. a doublet of periculous.
Etymology from Wiktionary, CC BY-SA