adverb
day by day; with each passing day
Describes a gradual change or increase that becomes more noticeable every day. Often used with verbs like 増す, 強まる, or 良くなる.
春が近づいて、一日増しに暖かくなっている。
As spring approaches, it's getting warmer day by day.
彼の病状は一
His condition is worsening with each passing day.