Boris Johnson called UK Labour leader a ‘mugwump’. Not even Boris Johnson knows what he meant

As Britain heads toward a snap general election, there’s one question on the minds of voters: What on Earth is a “mugwump”?

The query was prompted Wednesday by British Foreign Secretary Boris Johnson’s use of the word as an apparent insult in a newspaper column. Writing in the right-wing Sun tabloid, he attacked opposition leader Jeremy Corbyn, warning that the Labour candidate would not be able to stand up to threats such as “a revanchist Russia,” the “semi-deranged regime in North Korea,” and the Islamic State, which he referred to as “an evil Islamist death cult.”

Johnson argued that voters were underestimating the threat posed by Corbyn, an old-school leftist. “He may be a mutton-headed old mugwump, but he is probably harmless” is how the Conservative politician said concerns about Corbyn might be dismissed.

A mugwump? If you’re confused by that turn of phrase, you’re not alone. Although British political insults are often inventive - US President Donald Trump was once referred to as a “wazzock” in Parliament - “mugwump” may have been a bridge too far. The word quickly became a top search term in Britain, and there was widespread discussion of the word on social media.

But really, what is a mugwump? Even after consulting a dictionary, the answer isn’t completely clear.

The US Merriam-Webster dictionary offers two definitions: “A bolter from the Republican Party in 1884” or “a person who is independent (as in politics) or who remains undecided or neutral.”