Endless instances developed (9)
I believe the answer is:
incessant
'endless' is the definition.
(I've seen this before)
'instances developed' is the wordplay.
'developed' is an anagram indicator.
'instances' anagrammed gives 'INCESSANT'.
(Other definitions for incessant that I've seen before include "Nine casts (anag) - nonstop" , "Perpetual, unremitting" , "Since Stan was continual." , "Ceaseless" , "Instances being continually repeated" .)