(often + from/against) to protect (somebody or something) from attack
to attempt to retain (something that one holds, e.g. a military position, sporting title, or parliamentary seat) in the face of efforts by others to gain it
to maintain (something) by argument in the face of opposition or criticism
in sport, to attempt to prevent an opponent from scoring, e.g. by protecting a goal (e.g. a goal)
to act as legal representative in court for (somebody)
to take action against attack or challenge
to play or be in defence
defendable adj
defender noun
[Middle English defenden via Old French from Latin defendere, from de- + -fendere to strike]