False Friends

Anyone learning a foreign language soon becomes aware of false friends – those words that look alike in both the languages. One of the most obvious false friends in English for anyone learning it is actual. Most European languages seem to have a word that looks very much like it, but which means something different, usually ‘current’, or ‘present day’. But what about words that mean something quite different in different varieties of the same language? I’m thinking of words like alternate, that in British English means ‘every other’ – “He works on alternate days”, but in American English is an alternative word for – alternative. Many British airline passengers are disconcerted when an American pilot tells them they will be landing momentarily: they are expecting to be able to get off the plane. In British English, momentarily means ‘for a moment’, but in American English, ‘in a moment’. Warning signs on level crossings in Britain had to be changed after the authorities discovered that while has a different meaning in some parts of England. “Stop while the lights flash” was intended to mean that if the lights are flashing, stop, because a train is coming. But in some forms of English, the sign meant ‘stop until the lights flash’. Does this sort of false friend have a name?