Don't worry, meself; you were on the ball. The extract of Carroll's Preface (according to the same bit of Wikipedia) goes on to say;

"This also seems a fitting occasion to notice the other hard works in that poem. Humpty-Dumpty's theory, of two meanings packed into one word like a portmanteau, seems to me the right explanation for all.

For instance, take the two words "fuming" and "furious." Make up your mind that you will say both words, but leave it unsettled which you will say first. Now open your mouth and speak. If your thoughts incline ever so little towards " fuming," you will say "fuming-furious;" if they turn, by even a hair's breadth, towards "furious," you will say "furious-fuming;" but if you have the rarest of gifts, a perfectly balanced mind, you will say "frumious."

Cheers, Rowan