Debut of Michael Caine as criminal is one to forget (8)
I believe the answer is:
amnesiac
'one to forget' is the definition.
I know that 'forget' relates to this answer.
'debut of michael caine as criminal' is the wordplay.
'debut of' suggests taking the first letters (I've seen 'debut' mean this).
'criminal' indicates an anagram.
The initial letter of 'michael' is 'm'.
'm'+'caine'+'as'='mcaineas'
'mcaineas' is an anagram of 'AMNESIAC'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for amnesiac that I've seen before include "One suffers from memory loss" , "One quite forgets" , "Can't recall" , "Sufferer from clinical loss of memory" , "Person suffering from clinical loss of memory" .)