An extension number is the short internal number that reaches one desk. Dial the extension number, my extension number is 214, ask for the extension number.
It works only inside the building, and it saves the whole outside number being dialled. Direct dial has made it rarer, though switchboards still ask for one.
1nounextension numberThe short internal number that reaches one desk.
“Ring the main line and give them my extension number.”
extension number is a number.
Practised in Office & Admin