I've never met one, and most of my associations come from the beautiful SoCo song "Konstantine" - which refers, yes, to a girl.
People might know it as a male name from that terrible film "
Constantine", mind ... Assuming that was
Keanu Reeves' character's name and not some abstract reference. God, what a dreadful film ...
Either way (on either sex, I mean), I think you could pull it off. I like
Constantina as a middle name myself.
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♥
Elinor♥