Hit book for essayist (4)
I believe the answer is:
lamb
'essayist' is the definition.
(I've seen this before)
'hit book' is the wordplay.
'hit' becomes 'lam' (to 'lam' means to hit hard).
'book' becomes 'b'.
'lam'+'b'='LAMB'
'for' acts as a link.
(Other definitions for lamb that I've seen before include "Young creature" , "Tender sheep meat" , "Charles ---, essayist; meek animal" , "Mary, and Charles?" , "Skipper" .)