Correspondence
A link between a thing and a meaning, such as red and courage. A tradition, and no law of nature.
A correspondence is a link that tradition has drawn between a thing and a meaning: the colour red and courage, lavender and calm, Friday and love. Witches use correspondences to choose what goes into a working. Someone who wants to give herself courage takes a red candle and not a blue one, and the choice itself sharpens the intention.
The thought behind it is very old. It says that the world hangs together through likeness: the red of blood and fire stands for strength, a planet that moves slowly for patience. The scholars of the Renaissance collected such links in long lists. The best known is in the Three Books of Occult Philosophy by Heinrich Cornelius Agrippa, printed in 1533, in which every planet has its metals, plants, animals and colours. The tables in modern books of witchcraft go back to such lists, to folk custom and to their authors' own ideas.
A correspondence is a tradition and proves nothing. The tables contradict each other, and none of them says what a plant does to the body. If a colour or a scent means something else to you, your meaning is the one that works.
Related: the tables of the Grimoire, such as Colours and Herbs.