Yes, 'antecedents' can also be a word for back story. Antecedents are things that have happened or existed before a particular event or situation. When we talk about a character's antecedents, we are referring to their past experiences, family upbringing, and any events that have influenced who they are in the present, which is all part of their back story.
Some additional words for back story include 'preceding account' and 'prelude narrative'. The 'preceding account' is the story or information that comes before the main part. The 'prelude narrative' is like a prologue that sets the stage by providing the back story.
Sketch. This word can be used to refer to a short story as it gives the idea of a brief and often rough or unpolished piece of writing, similar to a quick sketch in art.
A farcical story. Farcical means something extremely funny in a rather absurd way.
Central figure. Just like in 'Romeo and Juliet', Romeo and Juliet are the central figures. They are the ones the story is mainly about, and their relationship and the events around it form the core of the play.
Family chronicle. It's like a record or account of family events over time.
Here are some other words for back story. 'Origin story' is one. It focuses on how something began which is related to the back story. 'Past events' is another simple way to refer to it. And 'historical context' can also be seen as a type of back story. The historical context provides the background information about the time period, the society, and the circumstances in which the main story takes place, which is very important for a full understanding of the story.
Yarn. This is a more informal way of referring to a story, often used when the story is a bit of a tall tale or something that might be exaggerated for entertainment purposes.
Narrative. It is a general term for a story, and when it's long and continuous, it can be used to describe what you're looking for.
'Spinning a yarn' is also a way to say telling a story. It has a more informal and perhaps even a bit of a creative or fanciful connotation. Sailors used to spin yarns (tell stories) about their adventures at sea, often with a touch of exaggeration to make the story more exciting.