Half of them love song of Horace, though it seems quite melancholy (4,4)
I believe the answer is:
long face
'half' is the definition.
Both the answer and definition are singular nouns.
Maybe there's a link between them I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for long face that I've seen before include "Unhappy expression" , "Elongated visage for dismal expression" , "expression of disappointment" .)