一いち日にち一いち日にち

adverb, adverb taking the 'to' particle

gradually; day by day

Describes a slow, steady change or progress happening each day. Often used with verbs of change like 変わる, 増える, 成長する.

• 春はるが近ちかづき、一いち日にち一いち日にちと暖あたたかくなってきた。

  As spring approaches, it's getting warmer day by day.

noun

every day; each day

Refers to each individual day as a unit, often in contexts of daily effort, routine, or counting days. More concrete than the adverbial sense.

• 一いち日にち一いち日にちを大たい切せつに生いきたい。