'Corylus' is the Roman name for the hazel and Linnaeus took 'avellana' from Leonhart Fuchs. Where he got the name 'avellana' from I am not sure. Somewhere (wikipedia, I think) it was stated that it was called that for the town of Avella, Italy but nowhere in Fuchs or Linnaeus does it state that. The Dictionary of English points to a town in Campagnia that may have been named for the apple, Abella. I wonder if 'corylus' (which is also spelt 'corulus') is related to the raven as a diminutive. This would make sense when one considers that Hugin and Munin (Thought and Memory) are two ravens, which sit on Odin's shoulders. There is nothing in the Oxford Latin Dictionary to support that connection. As well, 'æple' is one of the Old English forms for apple, Gaulish is 'avallo'(DOE) and so I was thinking that it was called 'the apple of the little raven'. The name 'hazel' comes from the Germanic; in Old English it is 'hæsel'.
I was reading Egil's Saga and the hazel was identified as an important sacred tree when it is used to stake out a formal battleground in Chapter 52. The battle staked out thus turns out to be the Battle of Brunaburh between King Aethelstan of the English and King Olaf with the Scots. As well, Egil laid a curse on the Norwegian king, Eirik Blood-ax, by placing a horse's head on a hazel pole and saying that the land-spirits shall have no rest until they drive Eirik out of Norway.
Donald Watts in his Dictionary of Plant Lore, states that the hazel is sacred to Thor, which I have to wonder about since he is already firmly identified with the oak and sometimes the mountain ash. How many sacred trees does Thor have? As well, its nuts are identified with wisdom, a quality that Thor is not usually credited with. He also says that it is a medieval symbol of fertility and perhaps this tree would be sacred to Frey then since he is a fertility god and as a Vanir, has suspected ties to witchcraft.
He points out that, in the original Grimm brothers' fairy tales, Cinderella did not have a fairy godmother but asked her father for a branch of whatever tree brushed against him on a trip and he brought home a hazel. Cinderella planted the hazel branch on her mother's grave and it becomes the source for her wish-fulfilment and power for revenge.
The hazel was also responsible for Finn McCool's wisdom in Celtic myth as the Tuatha de Danaan planted their nine hazels of inspiration and the knowledge of poetry at a well when they came to Innisfail. There is considerable overlap between Norse and Celtic mythologies, not surprising since they shared space and frequently fought or married one another. Poetry is a powerful tool for cursing and magic in both cultures. Hazel is supposed to be the twig by which St. Patrick drove the snakes out of Ireland and appears to be a powerful counter to fairy curses. This looks like an interesting book that I may want to order for myself.
Another really good resource on tree lore is Della Hooke's Trees in Anglo-Saxon England. It is expensive but I think, if you value accuracy, this is worth the price. Hooke adds that the hazel was used for divination and invisibility spells. Sacrificial victims like the Lindow bog-men were given crushed hazelnuts before they were killed. The hazel tree was frequently used as a boundary marker.
The holy family supposedly sheltered under a hazel tree when fleeing to Egypt. This puts the thought into my mind that, if the Tree of Life could be the Ash (Yggdrasil) then the Tree of Knowledge would be the hazel. Lucky me, I have one of these in my backyard. If only I could snatch the fruit before the squirrels get it. It is considered unlucky to pick the hazel; you are supposed to eat only the ones that fall to earth.
While I was researching this post, I discovered an online library, the Biodiversity Heritage Library which has Linnaeus's entire Species Plantarum online, see here.