From home, a tone is a sound you hear in music or in someone's voice.

Death means unable to hear.

So what could tone deaf mean as an idiom?

Oh, Jonathan Cynthia is so tone deaf.

She went to Duncan's party with peanut butter cookies and a big bag of peanuts.

What Duncan is allergic to nuts, his party invitation said, Please, no nuts.

And she missed that completely in everyday life.

Tone Deaf describes someone who doesn't notice how others think or feel.

They may seem a bit clueless about other people's situations and experiences, and that's English in a minute.