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 CarrollOne! two! and through and through The vorpal blade went snickersnack! He left it dead, and with its head He went galumphing back.
Lewis Carroll"It's very good jam," said the Queen. "Well, I don't want any to-day, at any rate." "You couldn't have it if you did want it," the Queen said. "The rule is jam tomorrow and jam yesterday but never jam to-day." "It must come sometimes to "jam to-day,""Alice objected. "No it can't," said the Queen. "It's jam every other day; to-day isn't any other day, you know." "I don't understand you," said Alice. "It's dreadfully confusing."
Lewis CarrollYou're thinking about something, my dear, and that makes you forget to talk. I can't tell you just now what the moral of that is, but I shall remember it in a bit." "Perhaps it hasn't one," Alice ventured to remark. "Tut, tut, child!" said the Duchess. "Everything's got a moral, if only you can find it.
Lewis Carroll