What's left without a memo (8)
I believe the answer is:
reminder
'memo' is the definition.
(thesaurus)
'what's left without a' is the wordplay.
'what's left' becomes 'remainder'.
'without' suggests deleting specific letters.
'remainder' with 'a' taken out is 'REMINDER'.
(Other definitions for reminder that I've seen before include "Memento" , "Memo - souvenir" , "Aide-mmoire" , "Memory refresher" , "Memory-jogger" .)