North Korea's leader Kim Jong-un makes a statement about Donald Trump's UN speech in a photo released by North Korea's news agency - REUTERS

Kim Jong-un’s latest broadside against Donald Trump had people across the globe reaching for a dictionary as he described the President as a “mentally deranged US dotard” in his latest outburst yesterday.

The antiquated expression is defined as “an old person, especially one who has become weak or senile”.

Merriam and Webster says in modern usage it commonly means “a person in his or her dotage”. It comes from the Middle English word doten (meaning "to dote"), which initially had the meaning of "imbecile" when it began being used in the 14th century.

�� 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

Mr Kim's remarks come after Mr Trump announced a new round of financial sanctions against the hermit nation on Thursday in response to its efforts to develop nuclear weapons and intercontinental ballistic missiles capable of reaching the US mainland.

In a statement released by the official Korean Central News Agency, the dictator described President Trump’s speech to the UN earlier this week as “unprecedented rude nonsense.”

Mr Kim also said: “I will make the man holding the prerogative of the supreme command in the US pay dearly for his speech.

“I am now thinking hard about what response he could have expected when he allowed such eccentric words to trip off his tongue. Whatever Trump might have expected, he will face results beyond his expectation.”

Mr Kim later added: “I will surely and definitely tame the mentally deranged US dotard with fire.”

The leader’s latest statement comes as he and President Trump have traded personal attacks and incendiary threats amid growing tension over North Korea’s nuclear programme.

Last week Mr Trump referred to Mr Kim as "rocket man" in a tweet, repeating the name in his UN speech on Tuesday when he also said the US would "totally destroy" North Korea if America or its allies were attacked.

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President Trump Making his speech to the Annual UN General Assembly in New York on Tuesday Credit: AFP

Pyongyang continues to defy mounting international pressure and UN sanctions to increase its nuclear capabilities. The state recently launch its sixth and largest nuclear test and fired a series of missiles over Japan.

Hours later after Mr Kim's latest statement the North Korean foreign minister, Ri Yong Ho, suggested Pyongyang could be considering a hydrogen bomb test on the Pacific Ocean of an unprecedented scale.

North Korea has said its aim is to develop missiles that can target the US mainland and announced it had tested a miniaturised H-bomb capable of being loaded onto a rocket earlier this month.

Yesterday President Trump met with the leaders of South Korea and Japan before unveiling tough new financial sanctions aimed at North Korea's trading partners.