Are all compound words nouns?

Some but not all compound words are nouns. Common compound nouns include “airport,” “grandparent,” “sandbox,” “yard sale,” and “merry-go-round.” Compound words can also be other parts of speech:

Compound words can be tricky because some of them are closed (one word with no hyphen), and others are open (two words) or hyphenated. Luckily, the QuillBot Grammar Checker can help you format compound words correctly.