also: じゅうねんいちにち
noun
unchanging for years; same old routine for a decade
A yojijukugo describing a state or attitude that has remained completely unchanged for ten years or a very long time. Often used critically to imply stagnation or lack of progress.
彼の生活は十年一日のごとく変わらない。
His life remains unchanged as if ten years were a single day.
その会社のやり方は十年一日で、革新がない。
The company's methods are the same old routine for a decade, with no innovation.