Here's why:
* Phrase head: This is a grammatical term that refers to the main word in a phrase, the word that determines the grammatical category of the whole phrase.
* Headword: This is the noun that describes the main word in a phrase, specifically the word that carries the central meaning.
For example, in the phrase "the big red car," the headword is "car," as it is the word that defines the category of the phrase (noun).