trying to explain to people what ideasthesia is is kinda difficult.
Because people already struggle with synesthesia, which is when two senses get crossed over. (ex: someone may taste colors, or see sounds). My friend who has it sees things as colors. But he has to physically see something with his eyes to see it as a color. Some people taste things when they touch them, or smell something when they hear it.
Ideasthesia is the same concept, but with ideas and concepts, things you cannot interpret with one of the five senses: eyesight, hearing, taste, touch and smell.
The day Monday isn't something you can interpret with one of the five senses. While you can exist within the day of Monday, you can't see, hear, touch, taste, or smell a Monday. You understand what Monday is, you can see the word Monday. You can have memories of a Monday. You can hear the word Monday. You can think about Monday, but you cannot interpret Monday by tasting the concept, hearing the concept, smelling the concept, touching the concept, or seeing the concept.
If you're brainstorming topics for an essay in your head, you can't see, hear, touch, taste, or smell that idea. You can visualize the topic in your head, but you cannot physically see it with your eyes.
To me. EVERYTHING has a color. The month of October is orange to me. You can exist in the month of October, but the concept of October is something you can't interpret with one of the five senses.
Some people have a hard time grasping at the concept of synesthesia- so getting people to separate that from ideasthesia can be near impossible sometimes.