A Necromancer in Warcraft is a robed
caster who utilizes Death, Shadow, Blood and Poison magic to debilitate and wipe out foes, while summoning the undead to keep enemies busy and distracted and themselves out of harms way.
A Death Knight in Warcraft is a heavily armored,
undead knight, raised from death by Necromancy, who utilizes Death, Shadow Blood and Frost magic to further strengthen his already mighty martial prowess, wading into combat to strike down foes with an unholy runeblade, while summoning undead to fight alongside themselves.
Let us break down those differences:
A Necromancer in Warcraft is not a knight.
A Necromancer is usually not undead, but can be (just as mages and warriors can be).
A Necromancer does not fight on the front lines.
A Necromancer does not wear heavy armor.
A Necromancer does not use a runeblade or runes, one of the single most iconic and core features of the Death Knight fantasy.
A Necromancer uses poisons and curses to great effect, summoning waves and eruptions and pools and novas.
A Necromancer has very little if any martial ability.
A Necromancer utilizes bone-based magic and summoning far more than Death Knights.
A Necromancer can use blood magic to empower and heal others rather than themself.
A Necromancer summons ghosts, wraiths, bone golems, specters, etc.
A Necromancer constantly summons an unceasing wave of low-health, temporary skeletal minions--this is the iconic ability of a Necromancer, which DKs do not have.
A Necromancer doesn't just attack the soul, they can rip it out to weaken enemies, call to the souls of the fallen to attack, harvest them to heal and empower, etc, etc.
A Necromancer is far more adept at weaving and using diseases to devastating effect.
A Necromancer can create Plague Cauldrons.
A Necromancer can become a Lich. Not use a simple spell named after them to counter feel, but become an actual, powerful skeletal magic user.
A Necromancer has an extremely
iconic look,
dress, and
facial appearance, both for
males and
females. Which is nothing like what Death Knights look like.
A Necromancer without their magic and minions is a sitting duck.