user10770: The name Semi-Slav suggests that somehow it's half of a Slav. How did this name come about? Or what does it mean? The two openings seem completely different to me due to the fate of the c8 bishop.

user21223: It simply because

With Black advancing pawns to both e6 and c6, the opening resembles a mixture of the Orthodox Queen's Gambit Declined (QGD) and the Slav Defense.

(from wikipedia)
If you consider that there are two components to the mainline Slav - protect the d5 pawn with c6 and then develop the light-squared bishop to f5/g4 - then the semi-Slav only shares one of these two features.

10770: <p>The name Semi-Slav suggests that somehow it's half of a Slav. How did this name come about? Or what does it mean? The two openings seem completely different to me due to the fate of the c8 bishop.</p>
 21223: <p>It simply because</p>
<blockquote>
<p>With Black advancing pawns to both e6 and c6, the opening resembles a mixture of the Orthodox Queen's Gambit Declined (QGD) and the Slav Defense.</p>
</blockquote>
<p>(from <a href="https://en.wikipedia.org/wiki/Semi-Slav_Defense" rel="noreferrer">wikipedia</a>)</p>
<p>If you consider that there are two components to the mainline Slav - protect the d5 pawn with c6 and then develop the light-squared bishop to f5/g4 - then the semi-Slav only shares one of these two features.</p>
