Where the last word of a sentence is irrelevant (6,3,5)
I believe the answer is:
beside the point
'irrelevant' is the definition.
(I've seen this in another clue)
'where the last word of a sentence is' is the wordplay.
I cannot really see how this works, but
an anagram of 'the' is 'eth' which is within the answer.
'last' could be 't' (I've seen this in other clues) and 't' is located in the answer.
'of' could be 'o' and 'o' is found in the answer.
'is' could be 'be' and 'be' is found 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 beside the point that I've seen before include "as the end of sentence?" , "Irrelevant" , "It's immaterial" , "Sentence starts or ends here" .)