I believe it's Samhain and pronounced sow (like the lady pig) wen (like the skin defect) or maybe sah-wen.

A little late coming into this thread but I thought I'd throw y hat in the ring since there was a call to the Celts.

You're almost right, Faldage. The spelling is Samhain and is pronounced Sa-wan with the a slightly lengthened like betwwen wan and wawn. The 'sa' sound is like 'sah' but more subtle and only slightly aspirated before moving onto the 'wan' part. It's almost like saying 'seven'. There's no major emphasis on either syllable.