A ‘portmanteau word’ (alias ‘blend’) is a word formed by blending sounds from two or more distinct words and combining their meanings, e. g., smog from smoke + fog. Apparently, the word portmanteau was first used in this meaning by Lewis Carroll in Through the Looking Glass: “Well, ‘slithy’ means ‘lithe and slimy’.‥ You see it’s like a portmanteau—there are two meanings packed up into one word.” The etymology (according to the Oxford English Dictionary Online) is from Middle French, French portemanteau ‘officer who carries the mantle of a person in a high position’ (1507 in Middle French), ‘case or bag for carrying clothing’ (1547), ‘clothes rack’ (1640) < porte- porte- comb. form + manteau manteau n. In the British English of Carroll’s time, a portmanteau was a suitcase. In modern French, a porte-manteau is a clothes valet, a coat-tree or similar article of furniture for hanging up jackets, hats, umbrellas, and the like.
As I sat contemplating my navel this morning, I suddenly remembered a portmanteau word created (with her nonpareil linguistic sprezzatura) by my late wife Marianne Shapiro to describe just my situation, namely moldiferate (mo[u]lder + proliferate), which is an intransitive verb meaning ‘to waste one’s time doing nothing while decomposing spiritually’. Another one of her creations in that vein is pestiferate (pestiferous + –ate), which she coined to mean ‘to cause to be pestiferous’. Neither word is in the OED, but they should be.