Father's herbal extract? (7)
I believe the answer is:
passage
'extract?' is the definition.
(extract is a kind of passage)
'father's herbal' is the wordplay.
'father's' becomes 'pa's' (pa can mean dad or father).
'herbal' becomes 'sage' (I can't justify this - if you can you should give a lot more credence to this answer).
'pas'+'sage'='PASSAGE'
Can you help me to learn more?
(Other definitions for passage that I've seen before include "Aisle" , "crossing" , "Excerpt" , "Way through; part of text" , "Transit - part of book etc" .)