Bone idle means extremely lazy. Although it looks as if it should have something to do with bones, the usual explanation is that it developed as a humorous alteration of born idle, meaning lazy by nature.
This kind of change is common in everyday speech. A familiar phrase gets reshaped into a new form that sounds similar but feels more vivid or memorable. In some accents, born and bone are close enough in sound for the switch to make sense. Over time, the altered version can become established in its own right.
For example, if someone says, He was too bone idle to cook, they mean he was so lazy that he would not even make food for himself. The phrase is informal and often slightly humorous, but it is still clearly critical.
- Meaning: extremely lazy
- Likely origin: a playful reshaping of born idle
- Tone: informal, sometimes comic, often disapproving
So the key point is simple: bone idle is best understood as a sound based twist on born idle, not as a literal reference to bones.