noun
ink line; carpenter's ink marker
A traditional carpenter's tool consisting of a small pot filled with ink-soaked cotton and a reel of string. The string is pulled through the ink and snapped against a surface to leave a straight line. The tool itself is often called an 'ink line' in English.
大工は墨壺を使って材木に直線を引いた。
The carpenter used an ink line to mark a straight line on the lumber.
noun
Refers to the pot or container that holds ink, especially in the context of the carpenter's tool. Not a general term for an inkwell used with a pen.
墨壺の中の墨が乾かないように蓋を閉めておく。
Keep the lid on the inkpot so the ink inside doesn't dry out.
Compound of 墨 (sumi, 'ink') and 壺 (tsubo, 'pot' or 'jar'). The word directly describes the tool's appearance and function.