Forgetfulness' is a name that changes (7)
I believe the answer is:
amnesia
'forgetfulness'' is the definition.
(I've seen this before)
'is a name that changes' is the wordplay.
'that changes' indicates an anagram.
'is'+'a'+'name'='isaname'
'isaname' anagrammed gives 'AMNESIA'.
(Other definitions for amnesia that I've seen before include "Mental condition" , "Is a name (anag.)" , "Clinical state of forgetfulness" , "memory problem" , "Inability to recall" .)