since (e.g. last month), for (e.g. 20 years)
Noun +
The suffix
Time Period Noun +
When attached to nouns representing a period of time, it indicates that a state has persisted throughout that duration.
ここ数日
I have been busy for the past few days.
これは十年
This is the heaviest rain in ten years.
彼とは年
I have known him for many years.
This grammar point is most commonly used with time-related nouns to indicate duration. It is often written with the kanji