tri-city

[ trahy-sit-ee, -sit-ee ]
/ ˈtraɪˈsɪt i, -ˌsɪt i /

adjective

of or relating to a metropolitan area consisting of three separate but interdependent cities: an instance of tri-city cooperation.

noun

any one of three such cities.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020