Witness eclipse (4)
I believe the answer is:
beat
'witness eclipse' is the definition.
The definition and answer can be both related to natural events as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
This is all the clue.
Can you help me to learn more?
(Other definitions for beat that I've seen before include "Policeman's regular route" , "buffet" , "Defeat, strike" , "Rhythmic music unit" , "cane" .)