noun
windowpane oyster
A species of oyster (Placuna placenta) known for its translucent shell, historically used as window glass in parts of Asia.
窓貝の殻は薄くて光を通すため、昔は窓に使われた。
The shell of the windowpane oyster is thin and lets light through, so it was used for windows in the past.
Compound of 窓 (mado, 'window') + 貝 (kai, 'shellfish'), referring to the traditional use of its translucent shell as a window pane.