Failure to remember polyphonic composition (5)
I believe the answer is:
fugue
I believe this is a double definition.
'failure to remember' is the first definition.
(as in a fugue state)
'polyphonic composition' is the second definition.
(I know that fugue is a type of polyphonic composition)
(Other definitions for fugue that I've seen before include "Composition involving a repeated interwoven melody" , "Strict musical form" , "Yearly records" , "One musical form ..." , "A musical form; a memory loss" .)