Gale's hiding book, a dictionary (8)
I believe the answer is:
websters
'gale's hiding book a dictionary' is the definition.
I can't judge whether this defines the answer.
'hiding book a dictionary' is the wordplay.
'hiding' is an insertion indicator.
'book' becomes 'b' (abbreviation for book).
'a dictionary' becomes 'westers' (I can't explain this - if you can you should give a lot more credence to this answer).
'b' going into 'westers' is 'WEBSTERS'.
Can you help me to learn more?
(Another definition for websters that I've seen is " In past times, weavers".)