Charming French endearment, first used as a name by Goethe, that now makes an appealing choice -- though the proper feminine form is Mignonne. Note, though, that this is not actually used as a name in France, where Manon would be the closest choice.
Mignon is the leading character, a young Italian dancer, in Goethe's novel Wilhelm Meister's Apprenticeship, upon which an eponymous opera was based. Mignon Eberhart was a popular American mystery writer.
The name is also associated with the flower name Mignonette.