box for ashes of the deceased; box for a funerary urn
Refers to a container used in funerary contexts, either directly holding cremated remains or holding an urn that contains them. Common in Buddhist and Shinto funeral practices.
After cremation, the remains are placed in a bone box.
I left the funeral hall carrying the box containing the urn.
Compound of 骨 (bone/ashes) and 箱 (box). The reading こつ for 骨 is the standard on'yomi used in many funeral-related terms.