Here are some examples:
* "The hikers faced a perilous journey through the treacherous mountain pass."
* "The ship sailed into perilous waters filled with hidden reefs."
* "The doctor warned about the perilous side effects of the experimental drug."
Synonyms for perilous include:
* Dangerous
* Hazardous
* Risky
* Threatening
* Precarious
* Treacherous
* Unsafe
Antonyms for perilous include:
* Safe
* Secure
* Harmless
* Non-threatening