Reserve quiet pixie some storage space (9)
I believe the answer is:
bookshelf
'some storage space' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'reserve quiet pixie' is the wordplay.
'reserve' becomes 'book' (to book something is to reserve it).
'quiet' becomes 'sh' ('sh' is used to tell someone to be quiet).
'pixie' becomes 'elf' (synonyms).
'book'+'sh'+'elf'='BOOKSHELF'
Can you help me to learn more?
(Other definitions for bookshelf that I've seen before include "It may hold great volumes?" , "Library furniture item" , "A supporter of literature?" , "Library support" , "supporter of literary works" .)