many years; long years
Refers to a long period of time that has passed or accumulated. Often used in formal or written contexts.
See also: 昔年
Years of effort have borne fruit.
A long-held dream came true.
noun which may take the genitive case particle 'no'
long-standing; ancient
Used attributively with の to describe something that has persisted for many years, especially negative feelings like grudges or hatred. The gloss 'ancient' is rare and mostly literary.
Long-standing resentment erupted.
Finally tackle a long-standing issue.