Synesthesia is when two senses combine with each other and form relationships. For example, I have the most common kind: grapheme-color synesthesia. Mine looks like this. The only one that’s supposed to be black is “1”. Otherwise, the ones in black have no color associated with them.
Lol! They don’t really bring up an association for me. Letters like W, J, and L eventually did, but they’re still pretty dim compared to the others.