Someone who will become an heir (usually to a monarchy) only if no-one with a higher-ranking claim is born.
A model or type of machinery or device which precedes the current (or later) one. Usually used to describe an earlier, outdated model.
One who precedes; one who has preceded another in any state, position, office, etc.; one whom another follows or comes after, in any office or position.
A vertex having a directed path to another vertex