India ink; China ink
Refers to the black ink used in East Asian calligraphy and painting, made from soot and glue.
We used India ink in calligraphy class.
Used for the dark liquid ejected by cephalopods like squid and cuttlefish.
Squid ink is sometimes used in cooking.
ink sac (of cephalopods)
Compound of 墨 (sumi, 'ink') and 汁 (shiru, 'juice, liquid'). The reading ぼくじゅう uses the on'yomi of both characters.