Well, the Titanic is the name of the ship that's at the center of the plot, so yeah, the meaning of the title is straightforward enough. Also, since the movie was such a gargantuan undertaking in terms of the filmmaking, it seems doubly appropriate.

That all said, would you be surprised to learn that Titanic wasn't the original title? We were. Cameron had originally planned to name the film—wait for it—Planet Ice (source).

If that seems absolutely ridiculous and implausible to you, it should—Titanic is a blockbuster and all that, but it's certainly not an intergalactic adventure. Relax: it seems that Planet Ice was just a code name to throw the press off of what Cameron was actually working on (source).

Clever, since the fake title made it sound like one of Cameron's more space-oriented movies, rather than a period piece/love story.