Definition of long-standing adjective from the Oxford Advanced Learner's Dictionary

 

long-standing

 adjective
adjective
BrE
 
; NAmE
 
[usually before noun]
 
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that has existed or lasted for a long time a long-standing relationship Long-standing grievances were aired at the meeting. The country’s long-standing relationship with the US was finally under strain.
See the Oxford Advanced American Dictionary entry: long-standing