taru-adjective, adverb taking the 'to' particle
entranced; in a daze; fascinated and distracted
Literary, old-fashioned word describing a state of being captivated or absent-minded, often with a dreamy or distracted air. Used with と (恍然と) or in たる form (恍然たる).
彼は美しい景色に恍然と見とれていた。
He was gazing entranced at the beautiful scenery.
恍然たる面持ちで音楽に聴き入る。
Listening to the music with a fascinated, dreamy expression.