Noun

• S: (n) central, telephone exchange, exchange (a workplace that serves as a telecommunications facility where lines from telephones can be connected together to permit communication)
• direct hyponym / full hyponym
• S: (n) centrex ((CENTRal EXchange) a kind of telephone exchange)
• S: (n) switchboard, patchboard, plugboard (telephone central where circuits are completed with patchcords)
• direct hypernym / inherited hypernym / sister term
• part holonym
• derivationally related form

Adjective

• S: (adj) cardinal, central, fundamental, key, primal (serving as an essential component) "a cardinal rule"; "the central cause of the problem"; "an example that was fundamental to the argument"; "computers are fundamental to modern industrial structure"
• S: (adj) central (in or near a center or constituting a center; the inner area) "a central position"