For example:
https://www.google.com/search?q=slang+dictionary+%22as+much+...
https://www.google.com/search?q=slang+dictionary+%22squeege%...
For some queries, Online Slang Dictionary even ranks above sites like Stack Exchange or Urban Dictionary. (Usually Urban Dictionary isn't so reputable, but for this sort of query, it's probably pretty relevant.)
What's the evidence here - some anonymous Google employee claimed the site was penalized back in 2013? That is not "hard confirmation" at all. Most likely, the site is not penalized at all. It just doesn't show up as often as Urban Dictionary and sites like english.stackexchange.com, and the operator is angry about that, but it honestly just isn't quite as good as those sites.