Double unity (3)
I believe the answer is:
two
This could be a double definition.
'double' is the first definition.
(thesaurus)
'unity' is the second definition.
The definition and answer can be both quantities as well as being singular nouns.
Perhaps there's a link between them I don't understand?
Can you help me to learn more?
(Other definitions for two that I've seen before include "A pair (3)" , "Number of faces of the god Janus" , "Minimal number of partners" , "Company, so it's said" , "Figure" .)