Part of book principal reportedly proscribed (8)
I believe the answer is:
headband
'part of book' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'principal reportedly proscribed' is the wordplay.
'principal' becomes 'head' (synonyms).
'reportedly' shows a homophone (sound like).
'proscribed' becomes 'banned' (banning is a kind of proscribing).
'banned' sounds like 'band'.
'head'+'band'='HEADBAND'
Can you help me to learn more?
(Other definitions for headband that I've seen before include "Something to secure the hair" , "Ribbon worn on top" , "fillet" .)