This question is inspired by this online dictionary of English that provides a way for people to find the possible words they are looking for by simply describing the concepts, a reverse dictionary as they address themselves. For an English-as-a-second-language person like me, such a resource is from time to time helpful in the sense that it scratches where it itches.
So I wonder if in somewhere there is a math dictionary designed likewise such that when we happen to not able to recall the common name of a property but its description then we can solve this problem by the dictionary.