a word that mash together the sounds and meanings of 2 other words. for example smog (a blend of smoke and fog) or infomercial ( a lenghty commercial chock-full of product information)

"Portmanteau word" is used to describe a linguistic blend, namely "a word formed by blending sounds from two or more distinct words and combining their meanings".

Such a definition of "portmanteau word" overlaps with the grammatical term contraction, and linguists avoid using the former term in such cases. As an example: the words do + not become the contraction don't, a single word that represents the meaning of the combined words.

The term “portmanteau word” was first used by Lewis Carroll in 1872 in the sixth chapter of favourite book for every English child”Through the Looking Glass”, to explain some words in the so called nonsense poem “Jabberwocky”: “Well ‘slithy’ means ‘lithe and slimy’ … you see it’s like a portmanteau - there are two meanings packed up into one word”, - says the author. And for us the meaning of the word is quite easier after its definition by Carroll.