Are you referring to what the French call a "window-door"?I am yet again being irritated by estate agents who call French windows French doors. Does anybody have any understanding of why this has crept into BE?
I understand that the term French door is used in AE, but we don't train our estate agents in the USA.
M. Viollet le Due, the great authority on French doors and their accompaniments, gives an account in his book of the manner of their fashioning from the twelfth century onwards.
But between two rooms they cannot be French windows (BE) or (presumably) French doors (AE) since the very essence of a French window is that it takes you out to the garden.1926 Daily Colonist (Victoria, Brit. Columbia) 18 July 11/5 (advt.) Thrown wide between two small rooms, French doors allow you the often convenient space of a large room.
But between two rooms they cannot be French windows (BE) or (presumably) French doors (AE) since the very essence of a French window is that it takes you out to the garden.
Interesting, the COED definition matches my understanding of the meaning, which I learnt at my father's knee (an architect):OED says a French door is the same as a French window.
A French window is:French window n. a pair of tall casement windows closing against each other with no frame between them, allowing access to the outside or to another room.