My favorite episode of the original Star Trek series, "The Gamesters of Triskelion," is about slavery. However, although the characters do occasionally refer to the situation using words like "slavery," the gamesters' preferred terminology for their prisoners appears to be "thralls." Moreover, when it comes time for Captain Kirk and his companions to be auctioned off, the gamesters do not refer to them as being "sold," but rather "vended."
These choices of less common synonyms for ordinary words have always struck me as peculiar. Is there any indication of why this was done? Was this a conscious choice by the screenwriter Margaret Armen, or perhaps by the producers, to give the episode a particular character?