That has been in existence for a long time(adjective)
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Use "long-established" in a sentence
""As fate would have it, I now give the order to case the colors," Gen. Austin said, referring to a long-established military ritual in which regiments "uncase" their identifying colors when arriving for deployments, and "case" them when they pack up to leave."
"This position is impossible to reconcile with the long-established view that Congress has the power of the purse."
"Many companies on the list are in the long-established IT category that venture capitalists have traditionally put their money into."