Well, "slithy" means "lithe and slimy." "Lithe" is the same as "active." You see it's like a portmanteau - there are two meanings packed up into one word.
Lewis CarrollIt takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!
Lewis CarrollI know who I WAS when I got up this morning, but I think I must have been changed several times since then
Lewis Carroll