Learn button on vocabulary.com does not show on all words

Question

Why is the Learn button not displayed in all word pages of vocabulary.com?

For example, on "whistle" it shows the Learn button on the sidebar area. But for another word, say troll, it doesn't.

Answer 1

Only words that have exercises written for them will show the Learn button. It's part of the challenge feature with understanding more of that particular word.

We’ve added a “Learn” button to show you which lists are ready to go. Clicking on the button will take you immediately to a Challenge that's tailored to the words you're interested in — anything from literary terms to words in the news.

Vocabularians Rejoice. List Learning is Here.

You are not seeing it on many words, e.g., "troll", because they have yet to write up a test or lesson to go with it that will help you understand and learn how to use the word.