I disagree with the previous person who has posted in stating that an assassin "may be motivated by financial gain, revenge, or personal public recognition or may be mentally ill." (He/she lifted that response verbatim from Wikipedia.) Those are definitions of what motivates murder, not assassination. It isn't assassination if there is not a policy motive. Although it would almost always involve a public figure, it might not necessarily involve a publicly known
figure. Killing the head of your enemy's intelligence services would remove someone who very likely is not
publicly known, but it would still be a good policy move, if successful.
"Does if have to be a holder of public office?" No. It could be any public figure--killing a monarch who rules by right of descent is killing someone who cannot reasonably be called a holder of a public office, but it still is a murder motivated by policy.
"Don't gangs assassinate opposing gang members?" Gang members murder
the members of opposing gangs, except perhaps in a rare case in which a gang leader were actually intelligent enough to have his opposing number assassinated for reasons of policy.
"Wasn't the Godfather assassinated, or was he merely murdered?" I would separate this from gangs, because street gangs don't rise to the level of organized crime. In the case of the godfather, i believe his murder was an act of revenge, rather than an act of policy. In that Michael Corleone assumed the leadership of that "family," if it were intended as a murder of policy, it failed.
"It doesn't seem to be important that money be involved, no paying hitmen or anything, right?" No, money doesn't necessarily need to be involved. It may be, but the determining factor is policy--i.e., is the murder motivated by policy.
"So, if I whack the mayor of my town, not that I have any intention of doing so and this is merely a hypothetical situation, because I don't like him it is murder, yet if I do so because I disagree with his political views it becomes an assassination?" That's kind of a tough one. It would likely be described as an assassination, but unless you had good reason to believe that he would be replaced by someone whose political views are consonant with your own, it could hardly be described as an act of policy--at the least it would be a failed attempt to manipulate policy.
"It would seem to me that some planning would need to be involved somewhere. You can't just have an off the cuff assassination. " Precisely.
We get the term from French. The "Old Man of the Mountain" and his assassins operated in the 11th and 12th centuries, at the time of the Crusades, and it was then that the word entered the French language. In French, meurtre
means murder, and that is where our word murder comes from. But the verb for the act of murder which is usually used is assassiner
--and occasionally, in some contexts, the noun assassinat
is used to mean murder. The distinctions are no more clear in English, but i would say that the preponderance of usage is toward killing for reasons of policy.
However, it would make a good distinction to explain this to your son.