Yes, urbandictionary, is a very trustworthy source, as you clearly can read on the description. ???? The other one you post above, does only have an explanation of another combination of the words you used. As do all other sources online.
Try using other sources like at least Wikipedia (However, very lose as all can contribute). There, the closest you will find is Fragile X Syndrome.
After that, try Britannica, Cambridge Lexicon and such sources.