Other forms: defended; defending; defends
Defend has different shades of meaning, but it always has the sense of protecting something — your ideas, for instance, or your title as world heavyweight champion.
If you order the blood sausage and lamb when you're out to eat with your vegan friends, you may have to defend your eating habits, meaning speak up in support of your choices. Defend can also be something more concrete, like when you defend your property or your country. The lawyer who represents someone accused of a crime is there to defend the accused person — who is called the defendant — and to argue his case in court.