Vanishing Spell: Might be something to render a person invisible or unnoticed, or another term for Apparation.
Vauxhall Road: A major thoroughfare in London. Tom Riddle bought a diary there.
Vector: Last name of the witch who teaches Arithmancy at Hogwarts.
Etym: From the mathematical term.
Venemous Tentacula: A spiky, dark red plant that has teeth.
Vernon Dursley: Etym: Alternative for vernal in 1658, or a surname derived from a common placename in France.
Veronica Smethley: Etym: Corrupted form of Latin vera icona, "true image". St. Veronica is a legendary figure who is said to have wiped perspiration from Jesus's face as he carried his cross; the cloth used retained an image. Also the name of a plant genus.
Vincent Crabbe: Etym: From a derivative of Latin vincens, "conquering". The name of a 3rd century martyr, and St. Vincent de Paul (1580-1660), remembered for his clinics and works of charity. A bit closer to the character we're talking about, also used in 1592 to mean the dupe in a betting game.
Vindictus Viridian: Etym: From the same root as vindictive and meaning pretty much the same thing.
Viridian, Vindictus (PS ch. 5): Author of Curses and Countercurses.
Etym: Strong green; technically, Veronese green. In this case, the green of jealousy or envy.
Voldemort: The Dark Lord; He Who Must Not Be Named. His rule was cut short by a curse that rebounded on him when he tried to kill the infant Harry and left him a shapeless wraith. Wand: 13 1/2", yew and phoenix feather.
Etym: Probably derived from French vol-de-mort, "flight of death". Beastly equation for "L*rd V*ld*m*rt": a=30, b=33, etc.
Voyages with Vampires: One of Gilderoy Lockhart's books.