(CNN) North Korean leader Kim Jong Un had some choice words for US President Donald Trump Friday, accusing the American leader of "mentally deranged behavior."

But it was Kim's use of the term "dotard," that has set the internet alight. While not widely used today, the insult is centuries old, appearing in medieval literature from the ninth century.

Searches for the term have spiked in the wake of Kim's address, according to dictionary Merriam-Webster, which defines the term as referring to "a state or period of senile decay marked by decline of mental poise."

Kim, of course, did not say the word -- he was speaking in Korean. "Dotard" was the official English translation provided by state news agency KCNA for the Korean "늙다리미치광이" ("neulg-dali-michigwang-i"), which literally translates as "old lunatic."

Later in the KCNA translation of Kim's address, the North Korean leader advises Trump to "exercise prudence in selecting words," something the news agency seems to have taken to heart.