If you think thats confusing, consider the word "Success."
In Gaelic a singular noun that begins in the letter C is pronounced with a K and a plural noun with an S.
Just paak your caaah in Haahvaad Yaad.....
It was my understanding that both pronunciations were correct.
Actually, Glasgow Celtic , the soccer club as a big Irish Catholic following. It was just that at the time there were a lot of illiterate Irish people, this was in the Victorian era,and this is where I have to surmise, the Irish who emigrated to the states took this name with them. The soccer part was in a Glasgow Celtic match programme
May have something to do with the fact Celtics are from Ireland while Seltics are from Beantown !!
'Cause they're from Boston.
... because long ago when the world was young, it was pronounced with the "s" sound prior to the general knowledge that the Celts pronounced with the "k" sound