Missing from those 3 charts is the one showing that citations were once again removed over 120 days ago, yet the penalty remains. It would appear that the algorithmic penalty was turned into a manual penalty.
I've followed all procedures including those listed in your comment, without resolution.
 By citations of slang use, I mean short (1-3 sentence) attributed excerpts of published works, shown within the appropriate definitions, as evidence of the correctness of those definitions. All citations were gathered and posted by hand.
Hi Walter, the only manual webspam action I see regarding onlineslangdictionary.com is from several years ago (are you familiar with a company called Web Build Pages or someone named Jim Boykin?), but that no longer applies here.
After trying for 1 year and 11 months to get anyone from Google to talk to me about the penalty, I can't tell you how ecstatic I am that you responded. Thank you! I would have responded sooner but I wanted to deploy some changes to the site, and also I was floored by some of the things in your comment and didn't know quite how to respond.
I'm very happy to read that there's no current manual action against onlineslangdictionary.com.
Hi Walter, the only manual webspam action I see regarding onlineslangdictionary.com is from several years ago...
Oh? I've never received a notice about having a penalty or about a penalty being removed. When was that penalty in place?
(are you familiar with a company called Web Build Pages or someone named Jim Boykin?)
Nope. I hadn't heard of either until I read your comment. Why do you ask? Did he/they cause the manual penalty against my site and then cause the manual penalty to be removed? How?
Interesting! I had read that post on the Webmaster Central Blog before, but never even considered that the layout algorithm was penalizing my site, for a few reasons. 1. The upper leaderboard ad + side wide skyscraper ad combination is so commonly used everywhere on the web. 2. I removed the leaderboard ad from the entire site from 11 May 2011 through 31 August 2011 and found it had no effect on the site's ranking. (It also had no effect on user behavior, such as bounce rate or time-on-site.) 3. My site isn't one of the sites "that go much further to load the top of the page with ads to an excessive degree or that make it hard to find the actual original content on the page."
I have removed all advertising from onlineslangdictionary.com, and also removed the yellow box at the top informing visitors why they no longer have access to the citations of slang use. (Better safe than sorry, I guess.) The page layout penalty should no longer be a problem.
(Since ads are no longer on my site, for reference, here are screenshots of those two URLs you linked, one from my site and one from urbandictionary.com:
I've read that article in the past, and gave it a re-read. I understand Panda is about penalizing low-quality sites.
High-quality dictionaries have citations of use from published sources. Citations prove the definitions are correct, provide real-world illustrations of proper usage, are just plain interesting, etc. Penalizing a dictionary for showing citations is like penalizing Wikipedia for having lots of numbered sentence fragments at the bottom of their articles. That's how they prove that their claims are factual.
Due to Panda, they were removed for non-authenticated users (including Googlebot) most recently starting 16 November 2012. They have been unavailable to authenticated users starting 8 March 2013. Because of a coding mistake on my part, they were visible for between 3 and 4 hours on 12 March 2013. (Basically: I accidentally inverted the logic of the 'if' statement that checks whether citations need to be removed (the answer should always be "yes") causing the code to not remove citations.) I fixed the bug as soon as I noticed it, and filed an updated reconsideration request.
The citations are gone. All content on the site is 100% original. It's got the only real, free slang thesaurus on the web. There are other unique features. I don't know what Panda would be penalizing the site for.
I started The Online Slang Dictionary in 1996, and have been working on it full-time for the past 6 years. My goal is to create the "Wiktionary of Slang" - not a flash-in-the-pan made-for-AdSense site. I was delighted with the site's ranking Between The Penalties: from 8 days after I first removed the citations until 3 days after I put them back on the site (13 November 2011 until 9 October 2012.)
It would be awesome to have the chance to once again compete on a level playing field with other slang websites. I'd love to have the time to implement the new features I've been dying to add, rather than spending time (over a year now) trying to guess why Google is penalizing the site and fixing those guesses - since my data shows that site growth is impossible with the penalties in place.
Hi, This is Jim Boykin. I have no records of ever doing anything for onlineslangdictionary.com ...but I guess it "no longer applies here"...but just strange that you'd associate me with this website...hum I wonder who else I'm associated with by google whom I have had nothing to do with...
P.S. One other quick thing. I saw you sending me tweets, but the tweets looked fairly repetitive, and you hadn't chosen a Twitter avatar. I get a lot of tweets from bots, and this looked fairly close to bot-like to me: https://twitter.com/mattcutts/status/315232934040846337/phot... That (plus the fact that the site had no current manual webspam actions, plus the fact that I wasn't sure what you meant by citations) meant that I didn't reply. Hope that helps.
Makes sense. All the tweets were by hand. I tried to tweet every weekday but missed some, then eventually gave up.
I just didn't know what to do upon getting no feedback from you guys after posting to the Google Webmaster forums, filing reconsideration requests, contacting friends at Google, posting to and commenting on Reddit about it, commenting on HN about it, posting to Facebook, blogging, and tweeting about it, and putting a yellow box at the top of all pages on the site mentioning the penalty and linking to a page with the details.