According to Wired's behind-the-scenes story on the launch, Facebook execs really didn't want the name to contain the word "search," because that makes people think of web searches.
Finally, they caved. Nothing else described the product as well.
“It’s descriptive — it’s search,” Zuckerberg explained to Wired's Steven Levy. “And the graph is a big thing.
"People use search engines to answer questions. But we can answer a set of questions that no one else can really answer. All those other services are indexing primarily public information, and stuff in Facebook isn’t out there in the world — it’s stuff that people share. There’s no real way to cut through the contents of what people are sharing, to fulfill big human needs about discovery, to find people you wouldn’t otherwise be connected with. And we thought we should do something about that. We’re the only service in the world that can do that.”