This name is probably a corruption of the word holy since this plant has been used from time immemorial as a protection against evil influence. It was hung around or planted near houses as a protection against lightning. Its common use at Christmas apparently originated in an ancient Roman festival in which holly was dedicated to the god Saturn. While the Romans were holding this feast—which occurred about the time of the winter solstice—they decked the outsides of their houses with holly. At the same time the Christians were quietly celebrating the birth of Christ, and to avoid detection they outwardly followed the custom of their heathen neighbors and decked their houses with holly as well. In this way holly came to be connected with Christmas customs. The plant was also regarded as a symbol of the Resurrection.
The use of mistletoe along with holly probably came from the notion that in winter the fairies took shelter under its leaves and that they protected all who sheltered the plant. The origin of kissing under the mistletoe is considered to have come from Saxon ancestors of the British, who regarded this plant as dedicated to Freya, the goddess of love.
hol·ly / ˈhälē/ • n. a widely distributed shrub, typically having prickly dark green leaves, small white flowers, and red berries. There are several deciduous species of holly but the evergreen hollies are more typical and familiar. • Genus Ilex, family Aquifoliaceae: many species, in particular the American holly (I. opaca), known as the "Christmas holly." See also gallbery, winterberry, yaupon. ∎ the branches, foliage, and berries of this plant used as Christmas decorations.
The holly as an evergreen tree is used as an image of fidelity.