Inability to remember a name is peculiar (7)
I believe the answer is:
amnesia
'inability to remember' is the definition.
(I've seen this before)
'a name is peculiar' is the wordplay.
'peculiar' is an anagram indicator (a peculiar or strange ordering of the letters).
'name'+'is'='nameis'
'nameis' is an anagram of 'mnesia'.
'a'+'mnesia'='AMNESIA'
(Other definitions for amnesia that I've seen before include "Mental condition" , "Am I sane? (anag)" , "Complaint" , "Asia men with memory loss (7)" , "Medical condition" .)