I think the word is used a bit too liberally these days. Some mystery/suspense authors label their books thrillers because thrillers sell better than mysteries.
I think we all know a thriller when we see one, though.
Here's my definition:
A fast-paced drama pushing the envelope of credibility with situation and character (the protagonist often possessing or attaining nearly or downright superhuman qualities and/or a super sense of duty/morality, pitted against a villain of equal or greater strength), where the stakes are increasingly raised and ultimately include a large group of people or even the entire world.
As opposed to the gritty realism of the harboiled/noir detective or the cute incompetence of the cozy's amateur sleuth, where one or a handful of lives are at stake, thrillers play more with suspension of disbelief and global consequences.
James Bond, for example, is the perfect hero. He's fast, witty, clever, a chick magnet, physically strong, an expert at EVERYTHING...
He's a super man, his world has a completely different set of rules than ours, and he's thrown into battles that are seemingly impossible to win.
That's what makes a thriller, IMO.
Thoughts?
What makes a book a thriller?