perilous
adj.full of danger or risk. You use this to describe a situation or journey that could be very harmful.
adj.fraught with danger or risk of injury, loss, or destruction. Often used in literary or formal contexts to describe physical journeys or precarious situations.
“The mountain climbers faced a perilous journey to the top.”
“The small boat made a perilous crossing through the stormy waters of the channel.”
“Navigating the narrow mountain pass during a blizzard proved to be a perilous undertaking that tested the limits of the team's endurance and equipment.”
Typically used attributively before a noun or predicatively after a linking verb like 'be' or 'become'.
“If anything, Grande is having a blast - teetering around in perilous heels, blowing kisses to the audience and embracing the physical and vocal demands of her show.”
“Academic research all over the world, including here in Australia, indicates young people are especially prone to loneliness and its perilous repercussions for mental and physical health.”
From Middle English perilous, from Old French perilleus, equivalent to peril + -ous, from the noun peril, or from Latin perīculōsus. Doublet of periculous.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.