A case or bag to carry clothing in while traveling, especially a leather trunk or suitcase that opens into two halves.1580s, "traveling case or bag for clothes and other necessaries," from Middle French portemanteau "traveling bag," originally "court official who carried a prince's mantle" (1540s), from porte, imperative of porter "to carry" + manteau "cloak".Portmanteau word "word blending the sound of two different words" (1882), coined by "Lewis Carroll" (Charles L. Dodgson, 1832-1898) for the sort of words he invented for "Jabberwocky," on notion of "two meanings packed up into one word."
From Wiktionary:
First used by Lewis Carroll in 1871, based on the concept of two words packed together, like a portmanteau (“a travelling case having two halves joined by a hinge”).A word which combines the meaning of two words (or, rarely, more than two words), formed by combining the words, usually, but not always, by adjoining the first part of one word and the last part of the other, the adjoining parts often having a common vowel; for example, smog, formed from smoke and fog.
From Vocabulary.com:
You might remember portmanteau from Lewis Carroll's Through the Looking Glass, where Humpty Dumpty explains to Alice the portmanteau word, in which "two meanings are packed up into one word." So, according to Humpty Dumpty, slithy means "lithe and slimy," and mimsy is "flimsy and miserable."