murder v. assassination

leave it to me to wonder about the requirements for a murder to be labeled an assassination. how important does a person have to be to be assassinated, rather than just plain old murdered?

the definitions are as follows:

mur·der: n. The unlawful killing of one human by another, especially with premeditated malice.

hom·i·cide: n. The killing of one person by another.

as·sassi·nation: n 1: an attack intended to ruin someone's reputation 2: murder of a public figure by surprise attack.

so i guess it is any public figure, regardless of import? am i not a figure in public? if someone were to shoot me, it would be a surprise.