I had never heard of it, yet we use it all the time ...Portmanteau :
A portmanteau or portmanteau word is used broadly to mean a blend of two (or more) words. A blend is a word formed from parts of two other words.
do + not = don’t , a single word that represents the meaning of the combined words.
breakfast + lunch = brunch
smoke + fog = smog
In 1964, the newly independent African republic of Tanganyika and Zanzibar chose the portmanteau word Tanzania as its name.
Bill Clinton + Hillary Rodham Clinton = Billary
Spanish + English = Spanglish
coined by Lewis Lewis Caroll in Through the Looking-Glass.
do not confuse with :
portemanteau : coat stand, coat rack
etymology : French- porte + manteau