day by day; every day; by the day
Describes a gradual change or a recurring daily occurrence. Often used with verbs indicating increase, decrease, or progress.
It's getting warmer day by day.
His Japanese is improving every day.
Standard kanji-kana mixed spelling; the most common written form.
Kanji spelling using 毎; less common but still encountered.
Compound of 日 (hi, 'day') + ごと (goto, 'every') + に (ni, adverbial particle). The ごと element indicates 'each' or 'every', forming an adverb meaning 'with each passing day'.