Memory loss -- a name is muddled (7)
I believe the answer is:
amnesia
'memory loss' is the definition.
(synonyms)
'a name is muddled' is the wordplay.
'muddled' indicates an anagram.
'name'+'is'='nameis'
'nameis' anagrammed gives 'mnesia'.
'a'+'mnesia'='AMNESIA'
(Other definitions for amnesia that I've seen before include "Clinical state of forgetfulness" , "Severe forgetfulness" , "Pathological forgetfulness" , "illness" , "Inability to recall" .)