What is the difference between tennis shoes and sneakers?

Ken, that is a fantastic question and I am delighted you asked. If I were to hazard a guess, I would say that tennis shoes are sold mainly for use on the tennis courts and probably have some kind of tricky, scientific design specifics that make them more suitable for the abrupt changes of direction and lateral movement inherent in the game that might blow other shoes out like a second-hand, high-mileage retread.

Sneakers, on the other hand, are most likely a rubber-soled shoe that would be worn by athletes and spies alike, who either need excellent traction or stealthy silence in their movement - hence the term "sneakers". I would also offer that the term "gumshoe" for the private eye probably came about from the requirement of stealth in the business of sleuthing. Whether or not a "gumshoe" is the same as "sneaker", I have no idea. I would also assert that a tennis shoe can be a sneaker, but a sneaker is not necessarily a tennis shoe. Let's go to the web...

"Sneakers go back a long way. In the late 18th century, people wore rubber soled shoes called plimsolls, but they were pretty crude—for one thing, there was no right foot or left foot. Around 1892, the U.S. Rubber Company came up with more comfortable rubber sneakers with canvas tops, called Keds. By 1917, these sneakers began to be mass produced. (They got the nickname sneakers because they were so quiet, a person wearing them could sneak up on someone.)" Ta-da, this from factmaster.com. I like the idea of the plimsoll - trying to differentiate between the left and right foot in the dark (especially scampering out a window with a jealous husband in hot-pursuit - just saying) can be trying. Plus, I think the plimsoll would make an excellent slapshoe, should one have the urge to be a circus clown or a silent film comedian.

And this from answers.com, regarding the gumshoe:

Gumshoe

(gŭm'shū')
n.

1. A sneaker or rubber overshoe.
2. Slang. An investigator, especially a detective.

I hope this answers your question - if it doesn't, feel free to hire a gumshoe to get to the bottom of it.

Good day, Sir.