The holly and the ivy,
When they are both full grown,
Of all trees that are in the wood,
The holly bears the crown.
Old Yule carol
As you might already suspect, our English word, “Holly” came from the same root word for “holy.”
For those of you who, like me, are fascinated with etymology, the New World Encyclopedia has this to say:
The origin of the word “holy” comes from the eleventh century Old High German hulis and Old English holegn meaning “Holly” as in Holly Tree, considered a sacred plant to both pre-Christian Celtic and Roman worship.
The word hulis originates from an even older proto-Germanic word khuli, a shortened derivation of the ancient Gaelic cuilieann, both meaning Holly.
The distinction of the word holy appeared around the thirteenth century with the Old English word hālig (derived from hāl meaning health, happiness and wholeness.)
As “wholeness,” holiness may be taken to indicate a state of religious completeness or perfection.
What a splendid and ancient spell-weaving lineage of language and words!
Holly’s Many Homes
Where I live in eastern North America, we have several native species of holly, both evergreen and deciduous. The crowning species, that is, the biggest tree, and the one we first think of when we say “holly,” is the prickly evergreen-leafed Ilex opaca, American holly, which is very similar to the English holly Ilex aquifolium.
Its very fine-grained white wood is beautiful for inlays (some of which can be seen in the elegant woodwork in colonial Williamsburg). 
The Ilex aquifolium (commonly known as English holly or European holly) is actually native not only to Britain, but also western and southern Europe, northwest Africa, and even southwest Asia.
Alas, along the west coast of the United States, from California to British Columbia, non-native English Holly has proven very invasive, quickly overtaking native forest habitat and crowding out other understory native species. 
It has been placed on the Washington State Noxious Weed Control Board’s monitor list, and is a Class C invasive plant in Portland.
Still, though, holly magic (preferably with your own native species) is powerful.
Magickal Holly
For centuries throughout Europe, holly has been believed to repel evil, and this belief lingers to the present day.
The old Pagan traditions of bringing holly boughs into the house in Winter, as a place for the Good Folk to play and protect the home, is echoed down to our own era, when holly wreaths are brought indoors for Christmas, to await the arrival of the Winter Elf King, now commonly known as Santa.
It was long regarded unlucky to leave holly wreaths up after Twelfth Night, so they were generally consigned to the fireplace on New Year’s Eve.
However, some felt that good luck could be obtained by keeping a sprig from a church’s holly wreath, so the church decorative wreaths would be divided among church members.
Western European Traditions
The Celts of the British Isles and Gaul believed the Holly King ruled over the dark half of the year (Winter), whereas the Oak King ruled the light and Summer. This ancient belief was preserved into medieval times through mummers’ plays, and has now been adapted into the neo-Druid and Pagan traditions.
The Holly King is often portrayed as a war-like giant bearing a great wooden club made of a thick holly branch.
He is also associated with Arthurian Legend as the Green Knight, who challenged Sir Gawain during a Yuletide feast, brandishing as his weapon “a solitary branch of holly.”
In Scandinavian mythology, the holly belongs to Thor and Freya. Tinne, pronounced CHIN-yuh, is the Ogham (in the Celtic Tree alphabet) associated with the month of the holly, and is the equivalent to dann or tan, a Celtic word for any sacred (holy) tree.
It is also related to Tannua, a Gaulish thunder God, who was associated with the dark Tanist God of the underworld. He is also more commonly known today by a variety of names such as the Green Man, Jack-in-the-Green and Robin Hood.
All are associated with the renewal of life following death, through the creative power of ancient tree magic.
Shinto Holly Traditions
Meanwhile, on the other side of the globe, in Shinto mythology, the Japanese holly (Ilex crenata) echoes the holly’s story in Europe.
When the Sun Goddess Amaterasu withdrew into her cavern and refused to come out, the erotic clown-goddess Uzume hung a sacred jewel and mirror in the branches of a holly. Then, as you may know, Uzume began to dance about the black-fruited holly tree in raunchy good humor, to attract the attention of Amaterasu and draw her out of the cavern so that life would return to the land.
Even today, a very popular Japanese good luck charm is a glass ball etched with holly leaves, symbolic of Amaterasu’s mirror, jewel, and tree.
In addition, a popular New Year’s charm consists of a holly leaf and skewer. This represents a story about the abundance God Daikoku.
Once when He was about to be attacked by an oni devil, His friendly companion rat hurried into the garden to fetch Him a holly branch, since an oni devil will not go near holly.
To this day, there is a tradition of hanging a holly sprig on the door to the house to keep away devils. How strikingly similar to the many holly-related beliefs in Europe!
I hope that you will take a walk in your woods or parks sometime soon, and find a holly tree to befriend. They are powerful allies and very good listeners. And they do love dancing Goddesses.
Merry blessings to all!