Defend, v. t. [imp. & p. p. Defended; p. pr. & vb. n. Defending.]
Etymology: [F. défendre, L. defendere; de- + fendere (only in comp.) to strike; perh. akin to Gr. dint. Cf. Dint, Defense, Fend.]
1. To ward or fend off; to drive back or away; to repel. [A Latinism & Obs.] Th' other strove for to defend The force of Vulcan with his might and main. Spenser.
2. To prohibit; to forbid. [Obs.] Chaucer. Which God defend that I should wring from him. Shak.
3. To repel danger or harm from; to protect; to secure against; attack; to maintain against force or argument; to uphold; to guard; as, to defend a town; to defend a cause; to defend character; to defend the absent; -- sometimes followed by from or against; as, to defend one's self from, or against, one's enemies. The lord mayor craves aid . . . to defend the city. Shak. God defend the right! Shak. A village near it was defended by the river. Clarendon.
4. (Law.)
2 more senses
To deny the right of the plaintiff in regard to (the suit, or the wrong charged); to oppose or resist, as a claim at law; to contest, as a suit. Burrill.
Syn. -- To Defend, Protect. To defend is literally to ward off; to protect is to cover so as to secure against approaching danger. We defend those who are attacked; we protect those who are liable to injury or invasion. A fortress is defended by its guns, and protected by its wall. As birds flying, so will the Lord of hosts defend Jerusalem; defending also he will deliver it. Is. xxxi. 5. Leave not the faithful side That gave thee being, still shades thee and protects. Milton.
Shades of meaning
Fernald has no entry of its own for defend; he lists it under keep, shelter.
Where he writes about it:
Keep in the sense of guard or defend implies that the defense is effectual. — from keep
That which covers may also defend or protect; thus, troops interposed between some portion of their own army and the enemy are often called a covering party. — from shelter
To defend (L. defendere, to strike away) implies the actual, protect (L. protegere, to cover before) implies the possible use of force or resisting power; guard implies sustained vigilance with readiness for conflict; we defend a person or thing against actual attack; we guard or protect against possible assault or injury. — from shelter
An inanimate object may protect, as a garment from cold; defend is used but rarely, and by somewhat violent metaphor, in such connection. — from shelter
Protect is more complete than guard or defend; an object may be faithfully guarded or bravely defended in vain, but that which is protected is secure. — from shelter
To shield is to interpose something over or before that which is assailed, so as to save from harm, and has a comparatively passive sense; one may guard another by standing armed at his side, defend him by fighting for him, or shield him from a missile or a blow by interposing his own person. — from shelter