So basically the word Luna has indeed Arabic origins, in Arabic the word Luna/Lawna means all types of date except for Ajwah, this name is not Popular in the Arab or Muslim World until the recent ages due to the western influence . But it is worldwide spread that the meaning of Lunas is Spanish/Latin meaning Moon, and it is directly realted to the Roman Goddess of Moon, and as we all know naming the Children after deities is HARAM, Abu Hurayra has changed his name from Abdul Shams (Servant of the Sun) to Abdul Rahman (servant of the most merciful). So I personally think that you should avoid this name even though t has an unpopular Arabic origin, If you want names like Luna but islamic, you can try Lina ( mentioned in Quran [59:5]) , Luha , Luza, Lubna (a Sahabi name) or Luma.