He atoned for his mistakes by apologizing to everyone affected.

He atones for his mistakes.

The atoners gathered to seek forgiveness for their past mistakes.

The atoner sought forgiveness for his past mistakes.

Atonalism is a challenging style of music composition.

The concert featured several atonalisms.

His actions were atonable and he sought forgiveness.

She spoke atonically, barely audible.

Atonicity is a characteristic of certain words in a language.

The patient had difficulty pronouncing the atonics in the word.