The juice of the nuts is used as an ink to marktextiles

marking-nuttree (pluralmarking-nut trees)

1. Any of several species of genusSemecarpus of trees.

• Indian marking-nut tree (Semecarpus anacardium)
• Malabar marking-nut tree (Holigarna arnottiana)

•  Semecarpus on Wikipedia.Wikipedia
•  Semecarpus on Wikispecies.Wikispecies
•  Category:Semecarpus on Wikimedia Commons.Wikimedia Commons