It can relate to an object such as an engine in a car when sitting at traffic lights. Then the engine is not in gear or under any load, therefore it is idle.

That he is idle might mean he is currently not working or refuses to work. Then it could be said he is bone idle which is to say he is any or all of lazy, or shiftless, even indolent

It could refer to the time when nothing is happening.

It could also refer to money in accounts not earning any interest

How many of us indulge in idle chatter, which is meaningless?

And how many of us have made an idle threat, especially to a child who refuses to go to bed, or sleep.

This is not to be confused with idol

An idol is generally thought of as a representation of a god, one used as an object of worship.

An idol can also be a person who is greatly admired, like a celebrity or superstar or a hero.

It could also be a figment of the imagination.

Then there is idyll which could be an extremely happy place, or a picturesque period or situation, one that is unsustainable

It could also be a short verse about rustic life.