three autumn months; three years
Literary term. Can refer to the three months of autumn (by the lunar calendar) or, by extension, three years. The 'three years' meaning comes from the idea of three autumns passing. Rare in modern everyday speech; mostly found in classical poetry and literature.
The word 'sanshū' appears in Chinese poetry.
The idiom 'ichijitsu sanshū' expresses that a single day feels as long as three years.
impatiently waiting; each moment feeling like an eternity
longing for loved ones
From Chinese 三秋 (sānqiū), literally 'three autumns.' The extended meaning 'three years' is based on the idea of three autumn seasons passing.