Douglas Harper's Etymology Dictionary
1846, from Irish Sile na gcioch, literally "Sheila of the breasts" [OED]. According to modern folklorists, not a Celtic survival, but originating rather in the Romanesque churches of France and northern Spain. Their theories that it is meant to degrade the female body and discourage sexuality, or that it is meant as an apotropaic gesture to ward off the devil, are not entirely convincing.
"Sheela-Na-Gig" is a song by English alternative rock singer-songwriter PJ Harvey, written solely by Harvey. The song was released as the second single from her debut studio album, Dry, in February 1992. The single was the second, and final, single from Dry and only single from the album to enter the charts in both the United Kingdom and United States. An accompanying music video, directed by Maria Mochnacz, was released alongside the single.