longstanding

from WordNet (r) 3.0 (2006)

longstanding
    adj 1: having existed for a long time; "a longstanding
           friendship"; "the longstanding conflict"

from The Collaborative International Dictionary of English v.0.48

long-standing \long-standing\ adj.
   existing since a time in the distant past; as, long-standing
   policies. [prenominal]

   Syn: longtime(prenominal).
        [WordNet 1.5]