Idle means not working, not active, or not being used. A factory machine sitting idle isn't running: it's switched off or waiting for someone to operate it. A car idling at a stoplight has its engine running but isn't going anywhere.

When applied to people, idle suggests someone isn't doing anything productive. A student sitting idle during study hall isn't reading, working on homework, or doing anything useful with their time. This kind of idleness implies wasted opportunity: the time could be spent learning something new or working toward a goal.

The word can also describe talk or thoughts that don't lead anywhere meaningful. Idle gossip is chatter about others that serves no real purpose. An idle threat is a warning someone makes but doesn't actually intend to carry out, like when someone says “I'm never speaking to you again!” but everyone knows they will.

People sometimes use idle to describe fears or worries that aren't based on real evidence. If you're anxious about failing a test you've studied hard for, someone might tell you not to worry about idle fears.

The word carries a mildly negative feeling: being idle suggests you're not making good use of your time or abilities. Someone described as an idler wastes time when they could be doing something worthwhile.