successive years; over the years
Used in formal or written contexts to describe something that has continued or accumulated over multiple years. Often appears as an adverb with に or in compound expressions.
The results of years of research were finally announced.
In this region, the population has been declining over the years.
Compound of 累 (accumulate) and 年 (year). The exact historical derivation is uncertain, but the word follows standard Sino-Japanese word formation patterns.