Dominic Smith was amused that the 07:55 journey from Cambridge called at "Letchworth, thence King's Cross".
He tweeted "wow" and said he had not seen the Middle English word used on a train platform before.
Greater Anglia, which manages the station, said it was a "one-off" and not a word staff would be using again.
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"The word 'thence' was added to one destination board this morning for the 07:55 Cambridge to King's Cross service. It is the first and last time it will be used at a Greater Anglia station," a spokeswoman for the operator said.
"It was a one-off and not a word we'll be using again."
The station manager had assured the company "thence" would not appear at the Cambridge station in the future, she added.
Dr Bettina Beinhoff, senior lecturer in applied linguistics and English language at Anglia Ruskin University, said: "According to the Oxford English Dictionary, thence is a Middle English word meaning 'from a place'.
"It is associated with archaic language and is now only occasionally used in formal contexts, so it is quite unexpected to see this word in such a modern setting."
The OED further classifies Middle English as the historical period spanning 1150 to 1500.
A train company has pledged never again to use archaic language after a commuter poked fun at the word "thence" on a departure board.