<p><em>This is a tweak / combination of two of @RichardHardy's answers <a href="https://stats.meta.stackexchange.com/a/4957/7290">here</a> and <a href="https://stats.meta.stackexchange.com/a/4956/7290">here</a>.</em></p>

<blockquote>
  <p>Let us keep <code>moving-average</code> for <em>moving average</em> (and include a warning about its use in the Wiki excerpt) and retag questions about <em>moving-average model</em> (MA(q) model) as <code>arima</code>.  </p>
</blockquote>

<p>In addition, we can create a new tag, <code>[moving-average-model]</code>, that will be made a synonym of <code>[arima]</code>.  An appropriate excerpt will need to be written for this tag.  Once it is made a synonym, anyone who uses it will have it automatically replaced by <code>[arima]</code>.  Note that there will have to be at least one question that remains tagged with <code>mam</code> so that the tag and its excerpt continues to show up when people type tag suggestions on questions.  Moreover, <code>mam</code> and <code>arima</code> would not be merged.  The point of leaving mapped tags unmerged is that the tag is more salient when someone searches on, say, "<code>movi</code>".  If the tags are merged, they will see "<code>[moving-average]</code> <code>[arima]</code>" as their options, and unless they read very carefully, and understand that a moving-average <em>model</em> is actually a special case of an ARIMA model, they would naturally choose <code>[moving-average]</code> incorrectly.  However, if the tags are not merged, <code>[moving-average-model]</code> <em>will</em> show up with its distinctive excerpt.  To further clarify how what people will see can differ, consider these two screenshots searching for a merged tag or a tag that is only a synonym: </p>

<p>Merged ("residual-analysis" is not very noticeable, and its excerpt is gone):   </p>

<p><a href="https://i.stack.imgur.com/4K9b6.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4K9b6.png" alt="merged"></a></p>

<p>Marked as synonym, but unmerged ("<code>[dataframe]</code>" is very salient; its excerpt is prominent; but it will silently be replaced by <code>[r]</code> if it is selected nonetheless):  </p>

<p><a href="https://i.stack.imgur.com/fCkjH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fCkjH.png" alt="unmerged"></a></p>

<p>Pros:</p>

<ul>
<li>Tag names reflect the underlying objects precisely.</li>
</ul>

<p>Cons:</p>

<ul>
<li>One tag name is an extension of the other, thus adding some confusion.</li>
</ul>
