to ward off attack from; guard against assault or injury (usually fol. by from or against): The sentry defended the gate against sudden attack.
to maintain by argument, evidence, etc.; uphold: She defended her claim successfully.
to contest (a legal charge, claim, etc.).
to serve as attorney for (a defendant): He has defended some of the most notorious criminals.
to support (an argument, theory, etc.) in the face of criticism; prove the validity of (a dissertation, thesis, or the like) by answering arguments and questions put by a committee of specialists.
to attempt to retain (a championship title, position, etc.), as in a competition against a challenger.