光阴荏苒

guāng yīn rěn rǎn

(idiom) How time flies!

光

guāng

light; ray (CL:道[dao4])

阴

yīn

variant of 陰|阴[yin1]

荏

rěn

beefsteak plant (Perilla frutescens)

苒

rǎn

luxuriant growth