A headword is the word or phrase that appears at the top of a dictionary entry, printed in bold or special formatting to show that it's the term being defined. When you look up magnificent in the dictionary, “magnificent” is the headword. When you search for solar system, those two words together form the headword.

Headwords organize dictionaries alphabetically so you can find what you're looking for. They're like chapter titles in a book: they tell you immediately what section you're in. Most dictionaries also show how to pronounce the headword and list its various forms (like how run becomes running or ran).

Lexicographers (the people who write dictionaries) carefully choose which words deserve to be headwords and which should simply appear within other entries. They might make basketball a headword but explain free throw within that entry instead.

When you're using a dictionary effectively, you're essentially jumping from headword to headword, using them as signposts to navigate through all the knowledge packed into those pages. Each headword is a doorway into understanding not just that word, but the ideas and concepts it represents.