Poster beginning to blog badly (4)
I believe the answer is:
bill
'poster' is the definition.
(synonyms)
'beginning to blog badly' is the wordplay.
'beginning to' suggests taking the first letters.
'badly' becomes 'i'll' (eg in ill-advised).
The first letter of 'blog' is 'b'.
'b'+'ill'='BILL'
(Other definitions for bill that I've seen before include "Account - legislation" , "Reckoning" , "Beak; poster" , "Poster' charge" , "parliamentary proposal" .)