The term for a word blending parts of two words, such as “brunch” from “breakfast” and “lunch,” is portmanteau.
A portmanteau combines fragments and meanings from two or more words. “Brunch” preserves the beginning of “breakfast” and the end of “lunch,” while “smog” joins “smoke” and “fog,” and “motel” combines “motor” and “hotel.” Linguists also commonly call these creations blend words.
The figurative use of portmanteau comes from Lewis Carroll’s Through the Looking-Glass, published in 1871. A portmanteau was a two-part travel case, and Carroll used it as a metaphor for packing two meanings into one word, especially in his poem “Jabberwocky.”
A blend is different from a compound word: “starfish” contains both original words in full, whereas a blend shortens at least one source. It is also different from a contraction such as “don’t,” which usually compresses words that commonly occur together.