"Aerys va oktiot dohaeriroso istas."

Translation: Aerys went to the city with a servant.

[DerGoldmann]

I suppose I could put "būzdaroso?" here interchangeably, right?

[avrichard]

I am guessing that dohaerir is any kind of servant, whether free or not, whereas būzdar is specifically a slave.

[purplepurpur]

Yes, you are correct. However, the course has up until now always accepted "slave" as a translation for "dohaeriros".

Correction: Buzdar, Dohaeriros

[ametris]

There are two words because buzdar(i) is a foreign word for slave/servant (it's from Astapori Valyrian not High Valyrian). You can tell it's a foreign word because the -ar(i) ending isn't native to High Valyrian.