noun, adverb
Describes something that happens or changes each day. Often used adverbially.
日ごとの気温の変化が大きい。
The daily temperature change is large.
彼は日ごとに上達している。
He is improving day by day.
毎日 is the most common word for 'every day' as a simple frequency. 日ごと emphasizes a gradual change or a daily occurrence in a more literary or descriptive tone.
Compound of 日 (hi, 'day') and 毎 (goto, 'every'). The reading ひごと is a regular rendaku form.