Important deal announced for part of propulsion system (8)
I believe the answer is:
mainsail
'propulsion system' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'important deal announced for part' is the wordplay.
'important' becomes 'main' (similar in meaning).
'deal announced for part' becomes 'sail' (I can't justify this - if you can you should give a lot more credence to this answer).
'main'+'sail'='MAINSAIL'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for mainsail that I've seen before include "Ian's mail (anagram)" , "The principal sheet on board" , "Lowest canvas on the principle mast" , "Ship's largest canvas" , "Principal ship's canvas" .)