Day divider (4)
I believe the answer is:
'day divider' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for noon that I've seen before include "Twelve o'clock in the day" , "Twelve during daylight" , "Twelve o'clock, midday" , "12 pm" , "The middle of the day" .)