Surprising success for nightmare? (4,5)
I believe the answer is:
dark horse
This might be a double definition.
'surprising success' is the first definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?
'nightmare?' is the second definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for dark horse that I've seen before include "Competitor about whose abilities little is known" , "Competitor whose abilities are unknown" , "Brown heroin" , "Little-known competitor like shadowy equine" , "unexpectedly successful entry" .)