Answer:
Two definitions: Not secure, or likely to fall OR Something that is uncertain or dependent on chance.
Step-by-step explanation:
It depends on the context of the sentence, but the most common definition is something that is not secure or likely to fall.
Sentence example: The book was precariously placed on the shelf.
Although, precarious could also mean something that is uncertain or dependent on chance.
Sentence example: She made a precarious living at working McDonalds.
I hope this helps you! :)