Wand - The magical instrument witches and wizards channel their powers through. Famous wand makers are Ollivander and Gregorovitch. A few examples of woods used to make wands are holly, sycamore, ebony, hawthorn, mahogany and elder. Known wand cores include phoenix feather, dragon heartstring, Veela hair and unicorn hair. When buying a wand, the wand should choose the wizard to achieve the best magical results.

Wand-Lighting Charm - Lumos. Wand movement: counter-clockwise loop. Creates a yellow glow (white if undercharged and scarlet if overcharged). Lights up dark areas and can be a defensive spell against many spectres and dark forces. To put the light out say Nox with a flick of the wand.

Wideye Potion - AKA Awakening Potion. A potion which prevents the drinker from falling asleep and can awaken those who have been drugged or have concussion. Can also be an antidote for the Draught of Living Death. 

Wiggenweld Potion - A healing potion which can awaken a person who has taken the Draught of Living Death and is in a magically-induced sleep. 

Wolfsbane - See 'Aconite'

Wormwood - A very bitter herb used in potion making. An infusion of wormwood is needed to brew the Draught of Living Death, Elixir to Induce Euphoria and the Shrinking Solution. Wormwood Essence is also, presumably, used in potion making.