The crossword solution for the term 'defunct car make' is GEO, a three-letter word. GEO was an American automobile marque that was produced by General Motors from 1989 to 1997. It was marketed as a subcompact car and was available in sedan, hatchback, and station wagon body styles. GEO vehicles were sold in the United States, Canada, Mexico, and the Middle East. The brand was discontinued in 1997 due to declining sales.