1. (noun)central, telephone exchange, exchange a workplace that serves as a telecommunications facility where lines from telephones can be connected together to permitcommunication
2. (adj)cardinal, central, fundamental, key, primal serving as an essentialcomponent "a cardinal rule"; "the central cause of the problem"; "an example that was fundamental to the argument"; "computers are fundamental to modern industrial structure"
3. (adj)central in or near a center or constituting a center; the inner area "a central position"