Humpty Dumpty explaining a couple words from Jabberwocky to Alice
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...
...Well then, 'mimsy' is 'flimsy and miserable' (there's another portmanteau for you).
From Through the Looking-Glass