Telephone extension is a term used to describe an additional telephone line that is connected to the main line. Synonyms that can be used to refer to a telephone extension include extension line, phone jack, extension cord, telephone wire, and additional phone line. These terms are commonly used in offices and homes where multiple people need to use the same phone line. An extension line allows individuals to make and receive calls from a different location without having to move the main phone set. The use of synonyms for telephone extension can help individuals to communicate clearly and effectively when discussing their phone systems.