People rowing with each other, one getting the wrong anniversary perhaps (9)
I believe the answer is:
eightieth
'people rowing' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'each other one getting the wrong anniversary perhaps' is the wordplay.
I cannot really see how this works, but
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
an anagram of 'the' is 'eth' which is within the answer.
'perhaps' could be 'eg' (for example) and 'eg' is present in the leftover letters.
This may be the basis of the clue (or it may be nonsense).
'with' acts as a link.
Can you help me to learn more?
(Other definitions for eightieth that I've seen before include "Tee it high (anag)" , "final day of circumnavigation" , "Ordinal number" , "A fraction equal to one-and-a-quarter percent" .)