One's book a little bit of poetry (4)
I believe the answer is:
iamb
'bit of poetry' is the definition.
(iamb is a type of metrical foot in poetry)
'one's book a little' is the wordplay.
'one's' becomes 'iam' (I can't explain this - if you can you should believe this answer much more).
'book' becomes 'bk'.
'a little' means to remove the last letter (the word is not quite complete).
'bk' with its last letter taken off is 'b'.
'iam'+'b'='IAMB'
Can you help me to learn more?
(Other definitions for iamb that I've seen before include "Poet's foot" , "Short-long metrical foot" , "Part of a pentameter?" , "Line of verse" , "Metrical unit" .)