INTERNATIONALLY celebrated sean-nos singer Aine Ui Cheallaigh made her unforgettable Broadway debut earlier this spring in the multimillion dollar Irish musical The Pirate Queen, produced by Moya Doherty and John McColgan of Riverdance fame.

Bringing her undeniably authentic Irish grace notes to Alain Boublil and Claude-Michel Schoenberg's score, Ui Cheallaigh lent the show, which is closing this Sunday, a Celtic gravitas that at times suggested she had been ushered in from an alternate and more venerable universe.

Classically trained by the legendary Irish voice coach Veronica Dunne, Ui Cheallaigh's high pure soprano voice established her reputation decades ago, and now her fan base genuinely is international. One can find superlative reviews of her work in every language (including Japanese).

Ui Cheallaigh first made her reputation as a sean-nos singer in the 1970s. Sean-nos, a term first coined in 1904, translates roughly to "traditional singing (in the old style)," a term intended to differentiate it from the far more prevalent parlor-room vibrato style of that period.

First brought to international prominence in Riverdance, Ui Cheallaigh has found increasingly wider audiences through the exposure. But she started out simply enough.

Born and raised in Belfast to a gaeilgr (native Irish speaking) mother, she spent long idyllic summers in Co. Waterford. "We lived in a very Protestant area of Belfast and we never really talked about the Irish language. We were always very careful to keep our heads low," she said during a recent interview with the Irish Voice.

"So we didn't speak Irish at home, but my mother was a fluent speaker. Every summer we spent with her people in Waterford, and for a long time I didn't understand a word they were saying, until one day it just came. I think it was in my genes (both of Ui Cheallaigh's sons are sean-nos singers in their own right). Soon after I began to learn the language in a formal way at school and college."

As her interest in traditional music and singing deepened, Ui Cheallaigh became aware of the rich legacy her mother had passed on. "My mother loved everything traditional. She hadn't a great voice but she used to sing to us so it was always in my ears," she says.

"When I started to go to Connemara to learn Irish from all the old fellows there I fit in, even though I was only 15 at the time. It touched something in me. I knew I wanted to learn the language, I knew I wanted to sing."

Classical training with Veronica Dunne taught her operatic technical skill, but her heart simply wasn't in that field. "I did have my voice trained, and Veronica was a wonderful person - I learned how to breath with her, I learned technique - but I threw it all out the window when I started thinking about sean-nos, because it's a completely different set of production values that you have in your body."

Dunne's training however helped Ui Cheallaigh immeasurably on Broadway. "What I'm doing on Broadway is not sean-nos as such. The music written for The Pirate Queen is a mixture of a classical mezzo-alto voice with reference to sean-nos, so a classical training has been incredibly useful in my time here."

Ui Cheallaigh has brought her very considerable artistry to her role in The Pirate Queen, so much so that she can fill the theater with the astounding force of her voice, steering the audience toward a centuries old sound that lifts the whole endeavor to another plane.

Says Ui Cheallaigh, "I can't deny that the largest part of my humanity is Ireland and the language. I was blessed with a good voice and because my mother was so rooted in that Irish language community I had access to it all.

"It was my passion really. I didn't know that when I was growing up but I can call it that now. I lived for the summer, I lived for getting away from Belfast and for stepping into that other tradition."

Now that The Pirate Queen is closing, Ui Cheallaigh is contemplating the creative path before her. "It would be my dream to work in this business either as a straight actress or in musical theater. I'm going home in the beginning of July and I'm hoping to find an agent when I get there," she says.

"I have been building up a repertoire in musical theater and at this point I'm prepared to work anywhere that work will bring me."

(The Pirate Queen is playing until June 17 at the Hilton Theatre, 214 West 43rd Street.)