Paragon

A perfect diamond of 100 carats or more.

Mid-16th century: from obsolete French, from Italian paragone ‘touchstone to try good (gold) from bad’, from medieval Greek parakonē ‘whetstone’[1].

Also used as a figure of speech for a person or thing that is perfect or has an extremely large amount of a particular good characteristic[2].

Used in “The Mission of Jane” by Julian Lethbury while speaking about Jane. Mrs. Lethbury tries to convince her husband to adopt Jane and ensures that Jane is a healthy and quiet child and that she would not cause any trouble. To find out who the real parents of Jane are, Mr. Lethbury asks: “And to whom does the paragon belong?” (Wharton, “The Mission of Jane”), meaning that, according to his wife, Jane should be a perfect child.

Sources:

[1] Source

[2] Source

"The Mission of Jane"