Sometimes Shakespeare will repeat individual theme words throughout the play. In Macbeth the most frequent word is 'blood,' 'Blood' is a word with a multitude of meanings. At its most dramatic it refers to violence, something that's very prominent in the play. There is a lot of killing, a lot of blood seen, and the characters use the word in everything they say. It's here that Shakespeare invents the word 'bloody', turning 'blood' into an adjective for the first time. 'Blood' also refers to family, as in blood relatives. Macbeth is the cousin of Duncan, whom he murders.