Passage in part of course missing introduction (6)
I believe the answer is:
airway
'passage in part of course missing introduction' is the definition.
'airway' can be an answer for 'passage' (airway is a kind of passage). I am unsure of the 'in part of course missing introduction' bit.
'passage in part' is the wordplay.
'passage' becomes 'air passage' (air passage is a kind of passage).
'in part' becomes 'way' (way is a kind of part. I am not sure about the 'in' bit.).
'air'+'way'='AIRWAY'
Can you help me to learn more?
(Other definitions for airway that I've seen before include "Regular route of aircraft" , "Ventilation passage" , "Vent; flight route" , "radio channel" , "passage for inspiration" .)