Vicious... is for his lack of morals and his willingness to kill without a second thought.
Over-estimated... is for having every witch and wizard in Britain cower away for him in terror or awe.
Legendary... is for being famous, although not in a good way.
Dementors... is for forming an alliance with dementors.
Elated... is for his joy each time he thinks that he is about to kill Harry.
Malicious... is for, need I say, he is Voldemort, he thrives on malice.
Old-Fashioned... is for his belief that pure-bloods are the best, and that Muggleborns are inferior.
Repulsive... is for his Dark ways, filled with unthinkable horrors whose only purpose is to maim and kill.
Terrorist... is for terrorizing all of Britain's Wizarding population.