'Corne' is French word meaning horn. So it's a creature with a single, 'unique' horn. Not sure of the etymology of unicorn, but the french word is 'licorne', whatever 'li' means...
Slivia returned soon and was glad that Jack wasn't at the campsite, wanting to avoid any more awkwardness. By the time she and Rydel packed up the two tents, Jack was back with another unihorn deer.