Eihwaz doesn’t have an exactly letter or vowel correspondence. It’s sound is similar to the long “i” sound.
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, the yew tree, is the rune of connection. Not partnership or exchange, but the connection that lies in the center of all things, and connects all things together. In that sense, it is also a rune of defense, the defense being actively engaged in your environment, alert and aware to what is going on around you and able to respond to it, in essence, you are connected to your space. It is also a rune of magic, as it describes the connection between all things, and that is lies at the heart of most magic, often known as sympathy and contagion. That which is below is like that which is above, and that which is above, is like that which is below.In that Eihwaz is the connecting rune, it shows connections happening. What type of connections and with whom (or what) should be explored, but in a general sense, it indicates that doors are open, and access has been granted.