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North Korean dictator Kim Jong Un dusted off his dictionary and revived an old-fashioned word by calling President Donald Trump a "dotard" in a scathing statement.

Kim baffled many with his word choice (translated from Korean to English), prompting head-scratching and mass dictionary lookups.

Kim Jong Un calls Trump a mentally deranged U.S. dotard. Searches for 'dotard' are high as a kite. https://t.co/HztPoLSjXi — Merriam-Webster (@MerriamWebster) September 21, 2017

Shakespeare used it. And the word appeared in The New York Times in 1852.

So what is a "dotard"?

Pronounced (dough-terd), the word generally means an imbecile. It refers to "a person in his or her dotage," according to Merriam-Webster. "Dotage" means "a state or period of senile decay marked by decline of mental poise and alertness."

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Kim used the word in his statement, in which he also called the president a "frightened dog" and "mentally deranged" after Trump, during his speech on the U.N. floor on Tuesday, threatened to "totally destroy" North Korea.

The word dates back to the 14th century, when it was first used by Geoffrey Chaucer, who is known as "The Father of English Literature."

In his 1387 collection called "The Canterbury Tales," he wrote: "For certeyn, olde dotard, by youre leve, Ye shul have queynte right ynogh at eve."

Usage peaked around the late 1500s and mid-1600s and fell out of use until it spiked slightly in the mid-1800s, according to Google's Ngram Viewer, which tracks the use of words.

Shakespeare put it in his play "Much Ado About Nothing," published in 1623, when a character says: "I speak not like a dotard nor a fool."

Kim used the word "neukdari," which in Korean translates to an "aged (old) person" and a "dotard," according to the Associated Press.

Jacques A. Bailly, a professor of classics at the University of Vermont who teaches etymology, told NBC News that the word is "an old fuddy-duddy," but has always meant a foolish person.

"I think of it as related to dotage. If someone was in their 'dotage', it is someone who was childlike in old age because of degeneration or disease," he said.

“It comes from the word ‘to dote’ which means to talk foolish,” he added.

The added -ard suffix is related to being associated with something or performing an action. For example, Bailly said, a wizard or drunkard.

Bailly said it's difficult to pinpoint why the word fell out of popularity.

"It’s not terribly obscure, (but) it probably doesn’t occur much in novels or newspapers," he added. "If I came to school...and called the gym teacher a 'varmint' and the gym teacher is confused. All they're going to do is look it up. That’s the case with dotard."