Final answer:
The term 'humbug' was popularized by Charles Dickens's 'A Christmas Carol' in 1843 as a synonym for a prank or hoax, often expressing annoyance.
Step-by-step explanation:
The six-letter word that became a favored expression of curmudgeons everywhere, thanks to its inclusion in a popular novella in 1843, is humbug. This term was famously used by the character Ebenezer Scrooge in Charles Dickens's novella A Christmas Carol. The word "humbug" describes deceitful or false talk and is often used to express irritation or disapproval of something considered to be a hoax or fraud.