You may know the American English-language expression two bits from the musical/rhythmic riff, “shave and a haircut, two bits” or from the meaning of two-bit as something cheap or trivial. You may even know that in the United States, two bits is twenty-five cents, a quarter-dollar, so you might think that one bit is one-eight of a dollar. You would be right.
How did this linguistic oddity come to pass?
Back when the United States were British colonies, due to a coin shortage, the colonies tended to use a Spanish coin called a dollar, also known as a piece of eight because it was worth eight reales. The real coin had been circulating in Spain since medieval times, and because of the rich silver mines in Spanish colonies in Mexico and South America, during colonial times reales and Spanish dollars became common currency throughout the world. The one-eighth dollar coins became known as “bits” or parts of a dollar.
When the United States became an independent country, it started making its own silver dollars and smaller coins, including quarter-dollars, and the terminology for bits as eighths hung on for a couple of centuries. Language changes slower than currency.
As for Spanish, the only meaning of bit is another meaning for that word in English, a BInary digiT used in computer sciences. Spain stopped using reales in 1868, when it replaced them with the peseta, until that was replaced by the euro in 2002.