noun
purple willow
Refers to the plant Salix purpurea. This literal sense is rare in everyday conversation; the word is far more common in the metaphorical expression 蒲柳の質.
蒲柳は水辺に生える柳の一種である。
The purple willow is a type of willow that grows near water.
noun
delicate constitution; infirmity
Almost always used in the set phrase 蒲柳の質 (ほりゅうのしつ), meaning a weak or frail body. The standalone noun use is very rare.
彼は蒲柳の質で、すぐに体調を崩してしまう。
He has a delicate constitution and easily falls ill.