A tincture is a trace or indication that reveals the presence of something. In pharmacology, a tincture is type of medicine extracted from a plant in an alcohol solution.
There are many meanings to the word tincture, but most of them involve something that leaves a trace or residue. A barrel-aged drink could have a tincture of oak. After a breakup, seeing an old flame could leave a tincture of sadness. When making drugs, a tincture is created by soaking a plant in an alcohol solution: traces of the plant are absorbed into the alcohol, creating medicine. The root is the Latin word tinctura, "act of dying or tingeing."