An abnormal growth or swelling that forms on oak trees and other plants, caused by insect larvae; historically used to make ink and dye.
From Old English 'galla' (from Latin 'galla') combined with 'nut.' These growths have been prized since ancient times—they contain tannic acid that was essential for making iron gall ink, which was used to write the Constitution.
Medieval monks used ink made from gallnuts to write manuscripts, and the same substance later produced the blue in blue jeans—a tiny tree growth literally preserved literature and revolutionized fashion.
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