What is the purpose of the silent “b” in doubt? Linguist Gina Cooke explains:
“Doubt” comes from the Latin word, dubitare. Once it spread to French, it lost the “b” sound, and became doute. In the 13th century, English scribes who understood Latin would reinsert the silent “b” into the English spelling, because the “b” signified connections with other words, like dubious and indubitably.
Another interesting side to “doubt” is its connection to the Latin word, double. When we doubt something, we are second (double) guessing ourselves, or acting of two (double) minds.
“Doubt” has one fascinating etymology — indubitably, of course.
(via TEDEd)