Inability to remember (7)
I believe the answer is:
amnesia
'inability to remember' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for amnesia that I've seen before include "Inability to remember" , "Seaman I found in state of memory loss" , "Defect in memory" , "Elephants won't suffer such" , "illness" .)