Rather fussy maker of stocking, including zip, put under chimney's opening (8)
I believe the answer is:
choosier
'rather fussy maker of stocking' is the definition.
I can't tell whether this defines the answer.
'including zip put under chimney's opening' is the wordplay.
'including' means one lot of letters goes inside another.
'zip' becomes 'o' (zip can mean zero).
'put' becomes 'hosier' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'under' means one lot of letters go next to another.
'opening' suggests taking the first letters.
The first letter of 'chimneys' is 'c'.
'o' inserted into 'hosier' is 'hoosier'.
'hoosier' put after 'c' is 'CHOOSIER'.
Can you help me to learn more?
(Other definitions for choosier that I've seen before include "more difficult to please" , "Harder to satisfy" .)