Sentence:  His uncle, a <WSD>Cardinal</WSD>, engages a Spanish youth of Moorish descent called Diego, an expert singer and player on the virginal, to unlock the secrets of the heart,...and cure him by the spell of his music. 
Meaning of the word marked with <WSD> tags:  One of the officials appointed by the pope in the (Roman Catholic Church), ranking only below the (pope) and the (patriarchs), constituting the special college which elects the pope.<ref>(date=17 Feb. 2014).</ref> (See Wikipedia article on Catholic cardinals.)