/lit/ - Literature

I need help carrying a piece of omitted exposition through a story. I want to research this through google, but I'm having trouble even finding like a trope name for this, so you don't have to spoonfeed me; just a name is fine.
I need my characters to occasionally reference, vaguely, The Bad Thing that happened to a character who dies because of it, without ever actually explaining what The Bad Thing was. It's not rape, but the character dies because of it, so it's clearly still fucked up.
Eventually, towards the end of the story, a relative of the "victim" takes revenge for it. The revenge does lots of damage to property, should come as a surprise to the reader and by the end of the story feel at least somewhat justified. The thing is, it's really important to me and the "tone" I'm going for, that I never explain what the original bad thing was.
It's mostly written already, but I don't have an editor, so I can't know if the lack of exposition on The Bad Thing is frustrating or makes the revenge insufficiently satisfying.
I'm sure this "omitted exposition" trope has a name, but I don't know what it is! I'd love to not have to bother y'all about this if I just knew what to googlefu. But, if you've read this and want to go a step further, I'm happy to take advice or book recommendations where this is done well. I want to do as much research on this as I can to really nail it, I just have to know what to look for.