"horrendous thing" is correct and usable in written English.
You can use it to describe something very bad or unpleasant. Example: "The news of the pandemic was a horrendous thing to hear."
"It's like losing a child … It's a horrendous thing.
She said the nature of her mother's death was "the most horrendous thing".
What was the last film you saw? Oh, I watched that horrendous thing.
When neighbours do that to one another, it is a horrendous thing.
Such dealers deserved to be "tarred and feathered, burned at the stake, castrated, and any other horrendous thing which can be imagined", editors opined.
Ms. Walker said she was moved: "She went through this horrendous thing and here she wants us to do a cookbook".
"What happened to me is probably the most horrendous, awful thing that could happen to a human being," she said.
Dictatorial regimes are doing horrendous things to their people in many places around the world.
You see people wearing the most horrendous, horrendous things that make absolutely no sense.
They concluded he probably had not initiated the horrendous things that happened, but merely allowed them.
"I accidentally liked this man on there and he sent me some really horrendous things.
