Notes anagram: I left one to be resolved (10)
I believe the answer is:
marginalia
'notes' is the definition.
(I've seen this before)
'anagram i left one to be resolved' is the wordplay.
'left' is a deletion indicator.
'one' becomes 'a' (a thing is one thing).
'to be' indicates anagramming the letters.
'resolved' becomes 'lia' (I can't justify this - if you can you should give a lot more credence to this answer).
'anagram'+'i'='anagrami'
'anagrami' with 'a' taken away is 'nagrami'.
'nagrami' is an anagram of 'margina'.
'margina'+'lia'='MARGINALIA'
Can you help me to learn more?
(Other definitions for marginalia that I've seen before include "Comments on the side" , "bits on the side" , "Notes written beside text" , "Notes written on the side" , "explaining letters put on one side" .)