noun which may take the genitive case particle 'no'
Used as a no-adjective to describe things that happen or are used on a daily basis.
I'm caught up in my daily life.
Refers to a period of days, often with a nostalgic or reflective tone, such as the days of one's youth.
I miss the days of my student life.
every day; day after day; day by day
Adverbial use emphasizing repetition or gradual change over time.
I'm growing day by day.
Her daily efforts finally paid off.
He is spending his days quietly.
This plant is growing bit by bit every day.
Society is changing day by day.
日々 usually means 'day after day' in a neutral, ongoing sense, while 日に日に stresses a visible change that grows or shrinks with each passing day.
ひび describes a fine hairline crack, especially in glass or ceramics, while 割れ目 refers to a wider, more visible split or gap.
Alternative spelling without the repetition mark; less common but still used.