Dark horse, say (5)
I believe the answer is:
night
This could be a double definition.
'dark' is the first definition.
(synonyms)
'horse say' is the second definition.
The answer and definition can be both states of affairs as well as being singular nouns.
Maybe they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for night that I've seen before include "Period of darkness" , "That's when it's darkest" , "For most, the time for sleep" , "From dusk until dawn" , "Dark hours" .)