Donald Trump claims to have invented the phrase "priming the pump".

The expression – which appears to have been in use for at least 200 years – was made up by the 70-year-old President, he claimed.

"We have to prime the pump," he told The Economist while trying to explain his economic philosophy, before asking whether the magazine had ever heard of such an expression.

"Have you heard that expression used before?" he asked the magazine. "Because I haven't heard it. I mean, I just... I came up with it a couple of days ago and I thought it was good. It's what you have to do."

The Economist's writer appeared to be about to correct Mr Trump. But he continued talking about the fact that "what you have to do is you have to put something in before you can get something out", and the opportunity passed.

However, the Merriam-Webster dictionary pointed out the phrase "priming the pump" actually dates to the early 19th century. It has been used to refer to government expenditure programmes – the exact thing Mr Trump claimed had never been said before – since at least 1933.

The dictionary never made explicit reference to Mr Trump's comments. But it did send a range of tweets about the history of the phrase.