Stands by for callers at Christmas (5)
I believe the answer is:
waits
'stands by' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for waits that I've seen before include "Night-time Yuletide singers" , "Stays" , "Itinerant carol-singers" , "Carol singers" , "Street performers at Christmas" .)