Aranrhod, and Culhwch, whose step-mother places a taboo on him that causes his famous quest for Olwen.

Even until recent times the Celts were keenly observant of taboos. None has been more interesting than their perception of the stars and planets. The power of the word was always uppermost in Celtic perception, and Dr. Tomás De Bhaldraithe, compiler of the modern Irish Dictionary, has argued that the names given to planets were forbidden druidic words so that the ordinary people could only refer to them by euphemisms. In Irish, for example, gealach (brightness) is the popularly used word for the moon. Other words exist as well. Old Irish contains ésca (aesca), and this word still survives in the Manx form as eayst but nowhere else. Another Irish word for moon was ré, and this, too, survives in Manx used as a combined word with that for light, shollys, in the word rehollys (moonlight). And yet another Irish word for moon, lúan, is now used as An Lúan as the name of the moon-day, or Monday. This word is thought to derive from the native Irish word for “radiance” rather than being a loan-word from the Latin luna. So here are four distinct words for moon, all being euphemisms rather than a proper name.

We can turn to Manx for a practical example of taboo names with this regard. In the nineteenth century, when Manx fishermen set foot on shipboard they were under a taboo (a superstition imposed by folklore) not to use the word eayst for moon until they returned to land. Until then they would refer to the moon as ben-reine ny hoie (queen of the night). Likewise, the sun was only referred to as gloyr na laa (glory of the day) and not as grian. In Old and Middle Irish we find several words for the sun also: as well as the modern word grian, we have ló-chrann (head of the day), still in use in Scottish Gaelic. The same word in modern Irish becomes the word for bright, brilliance, gleaming, guiding light, and leader. We also have ré-an-lá (light of the day), which is also used as ree yn lá.

It is interesting to note that while the ancient Celts (who were renowned for their ability in astronomy) must have had their own native names for the planets and stars, it is the Arabic, Greek, and Latin names that have been adopted into their languages. This supports the argument that there was initially a druidic proscription that continued into the period of early Christianity. Therefore,