砥と糞くそ

noun

grindstone sludge; sword-sharpening residue

Refers to the muddy, abrasive slurry produced when sharpening a blade on a whetstone. A technical or traditional craft term, not used in everyday conversation.

• 刀かたなを研といだあと、砥と糞くそをきれいに拭ふき取とる。

  After sharpening the sword, wipe off the grindstone sludge thoroughly.