noun
without thinking; innocently; unintentionally
Describes doing something casually, without deep thought or ulterior motive. Often used when an innocent remark or action leads to an unexpected result. Related to the adjective 何心無い.
See also: 何心無い
何心なく言った一言が彼を傷つけてしまった。
A casual remark I made without thinking ended up hurting him.
何心なく窓の外を見ると、雪が降り始めていた。
When I glanced out the window without any particular thought, it had started snowing.