The Powwow Guy

10 The third angel blew his trumpet, and a great star fell from heaven, blazing like a torch, and it fell on a third of the rivers and on the springs of water. 11 The name of the star is Wormwood.2 A third of the waters became wormwood, and many people died from the water, because it had been made bitter. Revelation 8:10-11

The Bible mentions wormwood nine times in total (8 in the OT, 1 in the NT). In all uses of the word, it is meant to be symbolic of poison and bitterness, especially in terms of water.

Historically, wormwood has been used to make a strong alcoholic brew called absinthe, which basically translates as "undrinkable" due to its horribly strong flavor and alcoholic content.

Wormwood can be taken internally in small doses for digestive issues. It has been experimented with for other medical reasons, such as liver disease, with varying results. It is also thought to induce sweating, which would seem to lend itself well to ridding the body of poison or toxins.

In Powwow, wormwood is often used to poison the magic of other magical practitioners, such as witches. This is most often done by "contaminating" an area with wormwood obscurely so that the offending witch will step over or through the area, thus rendering her magic useless while in the vicinity. To plant wormwood around your property is to also poison the magic that is sent your way. In essence, it protects you from the magic of others. 

One use of wormwood within the Powwow tradition is to fill a jar with dried wormwood then bury a piece of chalk in the herbs and seal the jar up. When you need magical protection, simply retrieve the chalk and draw your sigils or circle the put the chalk back into the jar for the next time you need it. Chalk absorbs the properties of the wormwood over time, making your chalk drawings as effective as using the herb itself.

Wormwood can be highly dangerous if you take too much of it internally, so I would definitely recommend limiting your usage to magical practice.

To carry a bit of wormwood with you is to negate any magic that is cast at you.