Shut up, dear, interrupting final... (8)
I believe the answer is:
enclosed
'shut' is the definition.
Both the answer and definition are adjectives. Perhaps there's an association between them I don't understand?
'up dear interrupting final' is the wordplay.
'up dear' becomes 'close' (similar in meaning. I am not sure about the 'up' bit.).
'interrupting' indicates putting letters inside.
'final' becomes 'end' (synonyms).
'close' placed inside 'end' is 'ENCLOSED'.
Can you help me to learn more?
(Other definitions for enclosed that I've seen before include "Surrounded completely, caged" , "Held" , "Confined" , "Shut up or included in an envelope" , "Inserted with letter" .)