Okay kiddo, cognitive synonymy is when two words mean the same thing in our brain. Imagine you're playing a game where you have to match pictures with words. If you see a picture of a dog and the word "puppy", you might also match it with the word "dog", because in your brain those two words mean the same thing.
So it's like having two special codes for the same thing. Just like how you might have a secret word that means "I'm hungry" and your friend has a different secret word that means the same thing.
But it's important to remember that not all words that seem similar are actually cognitive synonyms. Just because two words are synonyms in the dictionary doesn't mean they have the same meaning in our brains. It depends on how we use the words and what our experiences with them are.