In this chapter, you’ve learned how to categorize words according to their behaviour, which categories are open to new members, and which categories are not. You’ve also learned that compounding is a very productive means of deriving new words in English by combining two words. While most compounds are endocentric and have a head that determines the meaning and category of the word, for exocentric compounds, the meaning of the compound drifts over time, leaving the compound without a head.