いつとなく

いつしか, いつと(は)なく

＝いつのまにか.

●いつしか歳月が流れた. The years passed [slipped] by unnoticed. | The years and months rolled by before we knew it.

・彼はいつしかその教義を信じ込むようになっていた. Before realizing it, he had come to accept the teaching on blind faith.