栽 (zāi): The original meaning is “to plant” or “to cultivate,” like planting a tree (栽树, zāi shù). It can also mean “to stick something in.”
赃 (zāng): This character refers to stolen goods, illicit money, or a bribe. It's all about illegal or ill-gotten items.
When combined, 栽赃 (zāizāng) literally means “to plant stolen goods.” This vivid imagery perfectly captures the modern meaning: to secretly place incriminating evidence on an innocent person to make them appear guilty.