Fool blocking servant's way through (7)
I believe the answer is:
passage
'way through' is the definition.
(I've seen this before)
'fool blocking servant's' is the wordplay.
'fool' becomes 'ass' (ass is a kind of fool**).
'blocking' indicates putting letters inside.
'servant' becomes 'page' (I've seen this before).
'ass' placed within 'page' is 'PASSAGE'.
(Other definitions for passage that I've seen before include "Section of text; journey" , "course" , "Way through; part of text" , "Section of musical or literary work" , "Transit - part of book etc" .)