If something positive is “too much”, it becomes negative. For example, too much security could be perceived as being trapped.
Is there a term for this relation? In other words, if a word with a similar meaning is called a synonym, and a word with the opposite meaning is called an antonym, then a word with a negative extreme relation is called a ___?
Is there any kind of thesaurus to look these up?
I do not believe that a grammatical term exists for that. Terms like “synonym” and “antonym” exist because they describe relationships between words. On the other hand, the idea of something overly large or numerous describes an actual real-life condition. That falls within the province of vocabulary rather than grammar.
In other words, if someone told you “I am thinking of a word that is an antonym,” you would have no way of guessing the word they were thinking of. However, if someone told you “I am thinking of a word that describes something undesirably plentiful,” you could very reasonably guess “excessive.” There is no need for a grammatical term for that relation; it is contained within the word itself, and not a relationship between words. The term “excessive” is the description for the condition it describes.