What is a dotard? Kim Jong-un's archaic insult towards Donald Trump explained

North Korean leader deploys little-heard term in scathing attack on US President

North Korean leader Kim Jong-un delivers a statement in Pyongyang in response to Donald Trump's speech to the United Nations (AP)

Kim Jong-un's latest attack in an escalating war of words with Donald Trump sent people across the world to their dictionaries.

The North Korean leader branded the President a "mentally deranged US dotard" in a scathing speech delivered personally through state media.

Pyongyang is notorious for the bombastic, derogatory and often awkward English phrases it uses to lash out at enemies.

But Kim's use of "dotard" left many people scratching their heads.

The Oxford English Dictionary defines the word as "an old person, especially one who has become weak and senile".

Merriam-Webster gives "a person in his or her dotage," with dotage defined as "a state or period of senile decay marked by decline of mental poise and alertness".

The publisher said the word derived from the Middle English "doten" - meaning to dote - and originally meant "imbecile" when first used in the 14th century.

It added searches for the term were "sky high" on its website following Kim's speech, which was issued verbatim by Korean Central News Agency.

The agency reported that Kim said: "I will surely and definitely tame the mentally deranged US dotard with fire."

The Korean term used by Kim was "neukdari," which refers to elderly people in a derogatory manner. It translates literally as "old lunatic".

Kim's address, unusual in being delivered personally, came after after Mr Trump's speech at the UN this week in which he mocked the North Korean leader as a "Rocket Man" on a "suicide mission".

Social media users have poked fun at the feuding leaders.

"Rocket Man and Dotard meet in Nambia to avoid another Bowling Green Massacre," joked one, in reference to a non-existent country and fictitious terror attack previously mentioned by the Trump administration.