Not absent! Didn't I tell you so! (5)
I believe the answer is:
there
'you so' is the definition.
Both the answer and definition are adverbs. Perhaps they are linked in a way I don't understand?
'not absent didn't i tell' is the wordplay.
I cannot really see how this works, but
'not absent' could be 'here' (I've seen this in another clue) and 'here' is present in the answer.
A single letter 't' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for there that I've seen before include "In that respect" , "Yonder" , "on that issue" , "Thither" , "Expression of comfort" .)