Pinnacle of EastEnders that is almost the anniversary (9)
I believe the answer is:
eightieth
'pinnacle of eastenders that is almost' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'the anniversary' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'the' is 'eth' which is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for eightieth that I've seen before include "final day of circumnavigation" , "Ordinal number" , "A fraction equal to one-and-a-quarter percent" , "Tee it high (anag)" .)