Etymology:

Evil (adj.)

“Old English yfel (Kentish evel) “bad, vicious, ill, wicked,” from Proto-Germanic *ubilaz (cf. Old Saxon ubil, Old Frisian and Middle Dutch evel, Dutch euvel, Old High German ubil, German übel, Gothic ubils), from PIE *upelo-, from root *wap- (cf. Hittite huwapp- “evil”).”

“In OE., as in all the other early Teut. langs., exc. Scandinavian, this word is the most comprehensive adjectival expression of disapproval, dislike or disparagement” [OED]. Evil was the word the Anglo-Saxons used where we would use bad, cruel, unskillful, defective (adj.), or harm, crime, misfortune, disease (n.). The meaning “extreme moral wickedness” was in Old English, but did not become the main sense until 18c. Related: Evilly. Evil eye (Latin oculus malus) was Old English eage yfel. Evilchild is attested as an English surname from 13c.”

Literary Examples:

“That the contrary of a good is an evil is shown by induction: the contrary of health is disease, of courage, cowardice, and so on.”

~The Categories by Aristotle

“Before he was condemned they had often held discussions, in which they agreed that no man should either do evil, or return evil for evil, or betray the right.”

~Crito by Plato

“And nothing evil groweth in thee any longer, unless it be the evil that groweth out of the conflict of thy virtues.”

~Thus Spake Zarathustra: A Book For All And None by Friedrich Nietzsche

Common usage:

“The city has fallen on evil days.”

Evil, in it’s most modern and common usage is used to describe an action, person, or event so morally incomprehensible that no other word can describe  the malignancy of the action, person, or event. Evil is not simply an adjective or noun used in the English language, it is an idea as well, a summation of the malevolent half of the human conscience, the half that enables humans to murder and rape, the half that allowed the German populace to turn the other cheek and ignore the Holocaust, that allowed them to ignore the mass murders that occurred mere miles away from some of the biggest cities in Germany. It is an idea that was manipulated by philosophers such as Friedrich Nietzsche, Aristotle,  and Plato.  Our idea of Evil has sent men to war, it has motivated nations, and it has broken down great nations and people, the likes of which the world will never bear witness to again. Evil is the father, bringer and emperor of all human maladies.

“All concerns of men go wrong when they wish to cure evil with evil.”

~Sophocles , The Sons of Aleus

http://www.etymonline.com/index.php?term=evil&allowed_in_frame=0

http://www.thefreedictionary.com/evil

http://en.wikipedia.org/wiki/Evil

http://www.holocaustpictures.org/pictures/holocaust-pictures/holocaust.jpg.html