Etymology tree
Proto-Indo-European *lewk-
Proto-Indo-European *-sneh₂
Proto-Indo-European *lówksneh₂
Proto-Italic *louksnā
Latin lūna
Proto-Italic *-ālis
Latin -ālis
Latin -āris
Latin lūnāris
Old Galician-Portuguese lũar
Galician luar
Inherited from Old Galician-Portuguese lũar, from Latin lūnāris (“of the moon”). Compare Portuguese luar.