Portmanteau is itself a portmanteau word, from French.
porter ("to carry") + manteau ("a cloak") — to carry a cloak — it's a kind of suitcase that opens in two parts.
From Don Quixote
One of the students carried, wrapped up in a piece of green buckram by way of a portmanteau, what seemed to be a little linen and a couple of pairs of-ribbed stockings; the other carried nothing but a pair of new fencing-foils with buttons.
And from Frankenstein:
One night during my accustomed visit to the neighbouring wood where I collected my own food and brought home firing for my protectors, I found on the ground a leathern portmanteau containing several articles of dress and some books. I eagerly seized the prize and returned with it to my hovel. Fortunately the books were written in the language, the elements of which I had acquired at the cottage; they consisted of Paradise Lost, a volume of Plutarch's Lives, and the Sorrows of Werter.
Lewis Carroll first used portmanteau to describe a type of word in Through the Looking-Glass (1871), while Humpty-Dumpty is explaining the meaning of "The Jabberwocky."
It appears again in Carroll's Hunting of a Snark: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 . . . you will say "frumious."