This is not so much a question as an observation about a definition I read yesterday:

Merganser: a diving duck

Now this amused me because, if you look at the definition as being generic rather than specific, it would mean any diving duck would be a merganser.

You gotta be a pretty careful merganser when going after definitions. Definitions can be wily things when you bring 'em to the surface. They can get away from you!