Eihwaz is the vowel sound of the long I like “bite”. It actually does not get used often in runic inscriptions, and is often considered one of the more magical runes.
Anglo-saxon rune poem (from ragweedforge.com)
The yew is a tree with rough bark,
hard and fast in the earth, supported by its roots,a guardian of flame and a joy upon an estate.
Eihwaz means yew, a type of evergreen and a genus of tree that can be found in most of the northern hemisphere. It’s latin genus name is Taxus, because most of the tree is highly poisonous. It is also a very useful tree, as indicated in the poem (it burns well, lives long, has food for animals to eat (most berries by birds who are not affected by the poison). If you look up pictures online, it’s branches appear very twisty and gnarled, growing at different angles and changing direction. Yew wood also makes good material for constructing bows (for shooting arrows) and so yew trees were also favored for that reason as well. In Europe, most yew trees are found in graveyards, and so the yew is often associated with the dead, and the lands of the dead and so, the underworld.
In northern European lore about Yggdrasil, it is sometimes the Ash tree, sometimes a Yew tree. In my own personal work with it, Yggdrasil is both, and a few others. It is after all, the world tree. It can be many things. As yew tree, it is Yggdrasil as it connects to the underworld, but also Yggdrasil as the connector and ways between worlds. For that reason, it embodies the magical forces known as sympathy and contagion. Sympathy shows how plants, minerals, animal parts, symbols and other items share connections, and by working with one, you can influence the other. Contagion is the idea that things once in contact, maintain the link. It is, in a sense, the runic expression of that constant, and so it is a way to strengthen those bonds or weaken them.
It is in that same sense, a defense rune. In this case, it is the pushing apart of those connections, creating greater and greater distance. In a sense, creating that experience of being in the wrong place, a place that is incompatible with you, and ultimately a place that does not work well with who ever or whatever is being cast out from it.