Steak sandwiches mostly capital for one in the orchestra (8)
I believe the answer is:
trombone
'one in the orchestra' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'steak sandwiches mostly capital' is the wordplay.
'steak' becomes 'tbone' (T-bone steak is an example).
'sandwiches' is an insertion indicator (inserted letters are sandwiched in).
'mostly' means to remove the last letter (most but not all of the word).
'capital' becomes 'Rome' (capital of Italy).
'rome' with its last letter removed is 'rom'.
'tbone' placed around 'rom' is 'TROMBONE'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for trombone that I've seen before include "Brass instrument with sliding tubes" , "Brass musical instrument with slide" , "Musical instrument with long slide" , "Blow me!" , "Brass band instrument" .)