Meaning and etymology, from what I could find, are lost, but the name is likely of Gaelic origin. Naoise, pronounced either NAY-see or NEE-sha, in Celtic myth, was the ill-fated husband of Deirdre of the Sorrows (one of the stories in the legends called "Four Sorrows of Erin"). Deirdre was cursed so that only sorrow could come from her amazing beauty. She left Ireland with Naoise, fleeing to Scotland. But a jealous king there wanted her for himself, so they had no choice but to return to Ireland. There, Conchobar, king of Ulster, had Naoise and his brothers, Ardan and Ainle, murdered. While Deirdre was being taken away in a wagon, she stood so that her head was bashed against a tree, thus ending her sorrows. To modern practitioners of Celtic magick, Naoise can symbolise love and loyalty, while the three brothers together symbolise a male version of the Triple Goddess (maiden, mother, and crone) and Deirdre is a female version of the sacrificial god.