morning mushroom; ephemeral thing
Archaic term for a mushroom that appears in the morning and withers by night, used figuratively for something short-lived. Rare in modern Japanese; encountered mainly in classical literature.
朝菌 is used as a metaphor for something short-lived.
There is a poem that laments a life as fleeting as a morning mushroom.
From Chinese 朝菌 (zhāojùn), literally 'morning mushroom', used in classical Chinese texts such as Zhuangzi to symbolize extreme brevity of life. The Japanese reading ちょうきん is the on'yomi of the characters.