いっしんに
wholeheartedly; single-mindedly; fervently; intently
JLPT N1 Common word
Adverb
彼女かのじょは一心いっしんに祈いのっていた。
She was rapt in prayer.
そのピアニストの演奏えんそう中ちゅう、彼かれらは一心いっしんに耳みみを傾かたむけた。
They were all ears while the pianist was playing.