It’s of marginal significance (4)
I believe the answer is:
edge
'significance' is the definition.
The definition and answer can be both human attributes as well as being singular nouns.
Maybe you can see an association between them that I don't see?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for edge that I've seen before include "Move slowly" , "Surface boundary" , "Brim" , "The part farthest from the middle" , "Final line" .)