The word supercar later became to mean a GT or grand touring type of car. By the 1970s and 1980s the phrase was in regular use, if not precisely defined.
An advertisement for the Ensign Six, a 6.7 L high-performance car similar to the Bentley Speed Six, appeared in The Times for 11 November 1920 with the phrase If you are interested in a supercar, you cannot afford to ignore the claims of the Ensign 6. The Oxford English Dictionary also cites the use of the word in an advertisement for an unnamed car in The Motor dated 3 November 1920, The Supreme development of the British super-car. and defines the phrase as suggesting a car superior to all others. A book published by the Research Institute of America in 1944, that previewed the economic and industrial changes to occur after World War II, used the term supercar to describe future automobiles incorporating advances in design and technology such as flat floorpans and automatic transmissions. (source : wikipedia