Macbeth killed Banquo because he is the only one that suspects of Macbeth killing Duncan. One of the Witches´ prophecies was that Fleance, Banquo´s son would be King. So to prevent that and because Macbeth heard the prophecies aside with Banquo he decided to kill both of them.
-ive is a suffix that turns other words into adjectives. The verb Attract becomes attractive. Similarly to this, Respect can become respective, represent can become representative
