“A completely new word combining parts of two or more words. The word thus created expresses a combination of the meanings of its parts, as in the now common word brunch, created by combining the ‘br’ of breakfast with the ‘unch’ of lunch. Lewis Carroll introduced portmanteau words in Through the Looking Glass; he says slithy means lithe and slimy, mimsy means flimsy and miserable, etc. Carroll called the them portmanteau words because in them two meanings were ‘packed up’ in one bag, as it were. Modern writers have made liberal use of such words, notably James Joyce in his Finnegan’s Wake.”
Excerpted from: Murphy, Bruce, ed. Benet’s Reader’s Encyclopedia, Fourth Edition. New York: Harper Collins, 1996.