A poetic or literary term for the feeling of lovesickness, often evoking a classical or romantic tone. Not an everyday clinical term.
He was so afflicted with lovesickness that he couldn't even eat.
Many poems in the Man'yōshū sing of lovesickness.
Compound of 恋 (koi, 'love') and 草 (kusa, 'grass' or 'herb'), literally 'love grass'. The exact origin is uncertain; it may derive from classical poetic metaphor where love is likened to a plant that grows or causes suffering.