ふとした

pre-noun adjectival

impulsive; on a whim; casual; unexpected; accidental

Describes a sudden, unplanned, or chance action, thought, or occurrence. Often used with nouns like こと, 瞬間, きっかけ, 一言, and 出来事. The nuance ranges from a spontaneous whim to an inadvertent or unexpected event.

• ふとしたことで昔むかしの友とも達だちを思おもい出だした。

  I remembered an old friend by chance.