* Compound word: This is the most common term used when two words are joined together to form a new word with a single meaning. Examples: "sunlight" (sun + light), "birthday" (birth + day), "firefly" (fire + fly).
* Portmanteau: This refers specifically to a blend of two words, often using just a part of each word. Examples: "smog" (smoke + fog), "brunch" (breakfast + lunch), "spork" (spoon + fork).
* Blending: This is a broader term that encompasses both compound words and portmanteaus.
* Concatenation: This is a more technical term used in computer science, but it can be used to describe combining words in general.
* Hyphenated word: When two words are joined together with a hyphen, it can be called a hyphenated word. Examples: "well-being," "high-speed," "long-term."
The best term to use depends on the specific way the words are combined and the context in which they are used.