"Its thymidine, not thyamine (that is a vitamin)"
Actually, it's thymine. They're related thus says the Columbia Encyclopedia "Combined with the sugar deoxyribose in a glycosidic linkage, thymine forms a derivative called thymidine (a nucleoside)..."
True - I assumed his spelling was a bit generous regarding "thyamine" to be "thymine". But, as you correctly point out, Thymidine (that is the right spelling) is a derivative of Thymine.