Final answer:
The word 'humbug' refers to a 'prank or a hoax' and became popular in 1843. Originally an old nautical slang, it was often used to express skepticism toward deceptive or insincere acts.
Step-by-step explanation:
The six-letter word that became popular in 1843 and meant "prank or a hoax" is humbug:
The term humbug gained prominence and became a favored expression of curmudgeons everywhere following its inclusion in a popular novella of the time. Originally an old nautical slang, it conveyed the idea of something being a sham or deception. Its use in literature and common speech often implies a disdain for something considered to be misleading or insincere.
Throughout the 19th century, the word was frequently used by those skeptical of other people's intentions or of the era's many emerging novelties and perceived charlatans. For example, it could be directed towards fraudulent activities, dishonest schemes, or simply things that one found irreverently unimpressive. Over time, humbug maintained its negative connotations and even today is used in a similar context, although perhaps with less frequency than in its heyday.