Final answer:
A base word is 'a complete word that is part of another word,' serving as the foundation to which other word parts can be added to form new meanings, like in 'hypertension' where 'tension' is the base word.
Step-by-step explanation:
The phrase that describes a base word is 'a complete word that is part of another word.' A base word is a word that can stand alone and has meaning; it may serve as the foundation to which prefixes and suffixes can be attached to create new words. For instance, in the term 'hypertension,' 'tension' is the base word meaning pressure, and the prefix 'hyper-' is added to describe a condition of abnormally high pressure.
The concept of compound words further illustrates this: for example, 'dogcatcher' combines the base words 'dog' and 'catcher' to form a new word. Similarly, morphemes like the bound bases 'miss' and 'mit' reflect different forms or applications of base words in the construction of language.