According to an old European superstition, you should never cut your fingernails on a Sunday. If you did evil stories would be told about you for a week. Even worse the devil would follow you all week. Cutting fingernails was considered not only work, but also being preoccupied with your outer beauty. This was something that was not tolerated on the day of rest and worship.
Cutting your nails on a Friday was equally unlucky. It was said bad luck and sorrow would strike the home if anyone in the household dared to cut their fingernails on a Friday.
Friday and Sunday were certainly ruled out for cutting fingernails. Playing it safe, many would wait until Monday before cutting their nails. It was told that Monday before noon was a good time to bring out the scissors and cut those nails. Cut your fingernails early Monday morning and you could expect a gift. The saying went on like this. Cut on a Tuesday for thrift, cut on Wednesday for news, cut on Thursday for shoes, cut on Friday for sorrow, cut on Saturday to see your lover tomorrow, cut on Sunday for evil.
In the 19th century it was common superstition that if a mother cut the fingernails of her baby before the child was twelve months old, that child would grow up to become a thief.
Even the Vikings had strong concerns about fingernails. It was believed the ship called Naglfar (nail-ferry), was made solely from fingernails and toenails taken from dead humans. When Naglfar was completed, the Jotunns would sail this ship in battle against the gods. This was the final battle. This was Ragnarok, the end of the world. No dead man was to be buried with uncut fingernails. Every precaution had to be made to unsure that the corpse did not supply more material for building the Naglfar. But all was not lost. After Ragnarok a new world arises. Whatever happened to Naglfar, I do not know.