<p>I haven't investigated all questions using those tags; I go by recollection of having seen both used a few times recently.</p>

<p>What I recall seems to be consistent with 'terminology' being used in ways where 'definition' doesn't really fit, such as the sense "how should I refer to/describe/explain this?" type questions ... such as in <a href="https://stats.stackexchange.com/questions/126779/how-to-describe-a-bin-in-a-histogram">this recent question</a>.</p>

<p>... which use makes the two not-synonyms.</p>

<p>However, by suggesting that <code>definition</code> merge into <code>terminology</code>, you'd only need that <em>terminology</em> encompassed <em>definition</em> - and for that, there may be some argument.</p>

<p>I'd lean toward keeping them separate, but it's not something I feel strongly about.</p>
