Book with a weak line making you cry (4)
I believe the answer is:
bawl
'cry' is the definition.
(I know that bawl is a type of cry)
'book with a weak line' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'with' is a charade indicator (letters next to each other).
'weak' becomes 'w' (physics symbol as in W-boson).
'line' becomes 'l' (used when specifying particular lines from a poem).
'b'+'a'+'w'+'l'='BAWL'
'making you' acts as a link.
(Other definitions for bawl that I've seen before include "Loud shout" , "Cry loudly" , "Howl" , "Shout loudly" , "Weep noisily" .)