<p>I feel responsible because it was me who suggested this synonym; <a href="https://stats.meta.stackexchange.com/a/2866/28666">the suggestion</a> got several upvotes and was implemented in February (the respective answer is deleted so one needs 10k rep to see it).</p>

<p>At the time of merge, <a href="https://stats.stackexchange.com/questions/tagged/tikhonov-regularization" class="post-tag" title="show questions tagged &#39;tikhonov-regularization&#39;" rel="tag">tikhonov-regularization</a> had only 4 threads. Since then the synonym was not used a single time (<a href="https://stats.stackexchange.com/tags/synonyms">see here</a> in "Renames" column).</p>

<p>If you say that <em>Tikhonov regularization</em> in your field is understood to mean $$\|y-X\beta\|^2 + \|A\beta\|^2$$ with not necessarily $A=\lambda I$, then I agree that it is a bad synonym. It is also an almost useless synonym (it is practically never being used).</p>

<p>Therefore we might want to delete the synonym mapping and, as a result, stay without <a href="https://stats.stackexchange.com/questions/tagged/tikhonov-regularization" class="post-tag" title="show questions tagged &#39;tikhonov-regularization&#39;" rel="tag">tikhonov-regularization</a> tag.</p>

<p><strong>Update Oct 8th: The synonym mapping has been removed.</strong> There is currently no <code>[tikhonov-regularization]</code> tag. Anybody with sufficient reputation can re-create it; however there would only be a handful (3-5) of questions where this tag would be appropriate, see @Carl's answer from Sep 14th, and so in my opinion such a tag is currently not particularly needed.</p>
