You might also check this list of definitions from the Washington Post's coverage of olympic canoe and kayak events.

http://www.washingtonpost.com/wp-srv/sports/olympics/longterm/cankayak/canterms.htm

or check this page from the U.s. olympic canoe and kayak page:

http://www.olympic-usa.org/sports/az_3_9_4.html

The British probably have the simplest way of dealing with this: They call everything a canoe. When they want to talk about the open boats that Americans call 'canoes' they call them 'Canadian canoes'

Among kayaks there are many types: Whitewater, sea, Umiak, kayak, Baidarka, greenland styles, K-1, K-2, K-4, etc. Among canoes there are also several styles: Guide, sailing, square ended, whitewater, solo, tandem, C-1, C-2 and let us not forget similar craft, like pirogues, sculls, shells, and even dories. A large canoe, like a voyageurs canoe, or a war canoe, is even similar to a Viking long boat, a Venetian gondola, and a Chinese dragon boat.

The overall shape of the craft, and it's intended use, are major determining factors in indentification. Generally canoes have a higher rise at the bow and stern to keep out water, while kayaks, with a lower rise, have completely covered decks for the same purpose. A pirogue is frequently poled or rowed. A canoe is usually paddled with a single blade paddle, a dory may be sculled with a single oar, a shell is usually rowed with a pair of oars (or more) and a kayak is usually paddled with a double bladed paddle.

Again, these things are not absolutes. Gil Gilpatrick is pictured on his book poling his canoe, and a very popular little solo canoe (the Rushton designed, and oft imitated, Wee Lassie) was frequently propelled with a double blade paddle. Go figure!

And of course there are hybrids of these designs to make naming them more difficult.

Personally, I try to keep it simple. I call them boats.

Now, 'boat' may be a four letter word to some people, but I recall the difference between a boat and a ship: "A boat is what you get into when the ship sinks", and I find it comforting that I'm in a boat in the first place.

Paul G. Jacobson