a fluid for producing writing that is invisible until brought out by heat, chemicals, etc.; invisible ink.
Origin of sympathetic ink
First recorded in 1715–25
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for sympathetic ink
another term for invisible ink
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012