The term couch is predominantly used in Ireland, North America, South Africa and Australia, whereas the terms sofa and settee (U and non-U) are generally used in the United Kingdom. The word couch originated in Middle English from the Old French noun couche, which derived from the verb meaning "to lie down". It originally denoted an item of furniture for lying or sleeping on, somewhat like a chaise longue, but now refers to sofas in general.
The word sofa comes from Turkish and is derived from the Arabic word suffah ("ledge/bench"), cognates with the Aramaic word sippa ("mat"). Joseph Pubillones in A Little Shimmer Goes a Long Way specifies that the main difference between the couch and the sofa is that "couches can be used for reclining or laying upon" so a couch would "best be used to describe an upholstered piece in a family room", while the term sofa "used predominantly in England and Ireland denotes a tone of formality, hence a sofa is more appropriate word for the upholstered piece in the living room". The word settee or setee comes from the Old English word setl, which was used to describe long benches with high backs and arms, but is now generally used to describe upholstered seating. Other terms which can be synonymous with the above definition are chesterfield (Canada), divan, davenport, lounge, and canapé.