Are "gossip" and "rumour" perfect synonyms?

Are the words gossip and rumour perfect synonyms or is there a fine distinction between them? The only difference I'm aware of is that the second one is spelled differently in British and American English.

I'd say that rumor (as I spell it), like report or story, is a word denoting a particular type of narrative. This shows up in many constructions:

• It was reported that all lives were lost.
• It was rumored that all lives were lost.
• The story that she left him is untrue.
• The rumor that she left him is untrue.

It's not so much the spreading of the rumor, or the actual talking or writing, that rumor refers to; rather, it's the fact that there is talk, and more importantly, what the content of that talk is.

Gossip, on the other hand, denotes the social activity, and its participants, and their motives, and their strategies and tactics. The actual content of the talk is secondary to its perceived import, trajectory, and impact.

The nominalizations are telling: A gossip is a person -- A rumor is a story.

You can think of gossip as a particular case of rumor. Rumor is defined by dictionary.com as

a story or statement in general circulation without confirmation or certainty as to facts

Gossip, on the other hand, is defined as

idle talk or rumor, especially about the personal or private affairs of others (emphasis mine)

and usually has negative connotation.

For example,

Charles had bought along his hard redheaded wife Norma, and she was busy swapping malicious gossip with Emily.

The word rumor in the sentence above would be inappropriate. And here's an example of a sentence where gossip would be inappropriate:

Rumors of war were sweeping the country in the spring

I basically agree with Armen, but let me say it slightly differently:

A "rumor" is an unconfirmed story about any subject. "Gossip" is talk about other people's personal affairs. To some extent you could say that gossip is a subset of rumors. You could spread rumors that Al and Betty are having an affair, and you could spread gossip that Al and Betty are having an affair. But while you could spread rumors that the company is planning a layoff or that Senator Jones is considering running for president or that aliens are kidnapping people, you wouldn't normally call these things "gossip" as they aren't related to people's personal, private lives.

Also note that there are differences in how the words are used.

When used as a verb, "gossip" means to tell such stories. "Sally gossiped about the neighbors." "Rumor" as a verb is almost always preceded by "it is", as in, "It is rumored that the company is planning a layoff." You WOULDN'T say, "Bob rumors a lot."

"Gossip" can also be a collective noun referring to this type of story in general, like, "This so-called newspaper has more gossip than news." It can also refer to stories about a particular subject, but again is used as a collective noun. "There is a lot of gossip around town that Charlie is drinking again." When used as a countable noun "gossip" refers to a person: "She was a notorious gossip."

"Rumor" as a noun is countable, i.e. it is preceded by an article or indication of number. "There is a rumor that ..." "He spread many rumors." "I heard two rumors today ..."