sorrow of parting; parting grief
Literary noun for the sadness felt when separating from someone. Not an everyday conversational word; more common in poetry, lyrics, or formal writing.
His song is filled with the sorrow of parting.
駅のホームで友と別れるとき、ふと離愁を感じた。
When I parted from my friend on the station platform, I suddenly felt a pang of parting grief.
Compound of 離 (ri, 'separation') and 愁 (shū, 'grief, sorrow'). The exact historical derivation is uncertain, but the word is formed from classical Chinese elements and used in literary Japanese.