And here I was, thinking that poem was a string of brilliantly nonsencical made-up words.

No, no Grasshopper.

Jabberwocky is probably the world's premiere example of the use of portmanteau words. A brief Google search brought up this explanation that is much more succinct than any I could write myself:

"This term for blend word comes from portmanteau, a leather travelling case that opens into two hinged compartments (from the French for carry cloak), by way of Humpty Dumpty in Lewis Carroll's Through the Looking-Glass: "You see it's like a portmanteau -- there are two meanings packed up into one word."

"Although most modern blends are simply the first part of one word plus the last part of another (e.g., "brunch" = breakfast+lunch; "smog" = smoke+fog; "Chunnel" = Channel+tunnel), Carroll himself formed his portmanteau words in a more subtle manner: "slithy" = lithe+slimy; "mimsy = miserable+flimsy; "frumious" = fuming+furious. Carroll's coinages "chortle" (which is now in most dictionaries) and "galumph" (which is in the OED) are generally understood as chuckle+snort and gallop+triumph respectively, although Carroll himself never explained them."

Please -- do not underestimate the erstwhile Mr. Dodgson.

tanstaafl.