Druidism

These verses were communicated orally, and were never written down whilst bardism or druidism lasted, though the bards and druids at a very early period were acquainted with the use of letters. 

In this stronghold of druidism he resolved to celebrate the approaching festival of Easter, and preach the word to the assembled chiefs.

That last has received the name of druidism, from the druids who were its founders and priests.

Laeghaire Mac Neill—possessed druids and enchanters, who used to foretell through their druidism and through their paganism what was in the future for them.

Druidism was the religion of the Celts, and druidism was probably one of the least corrupt forms of paganism.