Composer's book appearance not OK (7)
I believe the answer is:
novello
'composer's' is the definition.
(I've seen this before)
'book appearance not ok' is the wordplay.
'book' becomes 'novel' (novel is a kind of book).
'appearance' becomes 'look' (look is a kind of appearance).
'not' suggests deleting specific letters.
'look' with 'ok' taken away is 'lo'.
'novel'+'lo'='NOVELLO'
(Other definitions for novello that I've seen before include "Ivor --, songwriter" , "Ivor --, composer/actor" , "popular composer" , "Ivor --, Welsh singer, actor, composer" , "he used to make up the numbers" .)