A really good reminder that Christmas is coming (7)
I believe the answer is:
cracker
'a really good reminder' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for cracker that I've seen before include "Great joke - terrible joke's container?" , "Biscuit -- firework" , "An outstanding example of its kind!" , "Xmas table extra" , "Knockout biscuit?" .)