The term Wormwood was first mentioned by Dean Winchester in 2.13 Houses of the Holy in reference to a type of vine. Wormwood is also used as an ingredient in 4.02 Are You There, God? It's Me, Dean Winchester to stop the Witnesses.
It's wormwood. Plant associated with the dead; specifically the ones that are not at rest. I don't see it growing anywhere else, except over the murdered priest's marker.
And there fell a great star from Heaven, burning like a torch. And it fell upon a river, and the the name of the star was Wormwood, and many men died.
- The name wormwood did actually appear in The Bible as a word of uncertain origin (Greek: apsinthos) which symbolizes a sort of bitterness, or figurative calamity.