counter
Poetic counter used after numbers in the classical hito-futa-mi counting system (e.g., ひととせ, ふたとせ). Not used in modern counting; replaced by 年 (ねん) or 年 (とし) in everyday language.
ひととせの思い出を胸に、旅立つ。
With memories of one year in my heart, I set off on a journey.
ふたとせの歳月が流れた。
Two years have passed.
Derived from the classical Japanese counter とせ, used with native Japanese numerals. The kanji 年 and 歳 are both associated with 'year' and 'age' respectively, but the reading とせ is now archaic and poetic.