Hatchets and tomahawks are both types of short axes, but generally seem to have one distinctive physical difference. For wooden handled tools, the tomahawk eye is usually larger and tapers outward at the end. Hatchets, like axes, taper inward if at all, and have smaller eyes.
This is a pretty broad generalization, and kinda breaks down when looking for specific examples. "French" axes, for example, would probably be called "tomahawks" in America, due to the similarity in construction. And all metal tomahawks/axes/hatchets follow no distinct rules. Several companies make a one piece tomahawk, and several others make a one piece hatchet. The difference is usually just aesthetic.
Tomahawks have a history of use as weapons. Of course, that doesn't mean a hatchet (or clawhammer, for that matter) can't be used as a weapon. Or a tomahawk as a chopping tool. In the end, if a manufacturer calls it's tool a hatchet, then it's a hatchet. If they call it a tomahawk, it's a tomahawk.
