Part lacks introduction in glowing piece (5)
I believe the answer is:
ember
This clue might be a double definition.
'part lacks introduction' is the first definition.
The answer and definition can be both natural objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'glowing piece' is the second definition.
(I've seen this in another clue)
'in' is the link.
Can you help me to learn more?
(Other definitions for ember that I've seen before include "Still smouldering fragment of wood or coal" , "Smouldering piece left over from a fire" , "Material in dying fire" , "Piece of live coal" , "Remnant of bonfire" .)