It was not enabled by default until the release of the first beta version of iOS 12. However, with second developer beta and public beta version, it is enabled by default. So, there are chances that it stays when iOS 12 gets released worldwide.
So, if you are writing an article or research paper, replacing phrase out for another word is easy with thesaurus enabled on your iPhone. When you use Look Up tool to check the phrase, you might get results from New Oxford American Dictionary or Apple Dictionary by default. If that happens, then you need to enable the thesaurus. However, if you get the Oxford American Writer’s Thesaurus, then it is already enabled on your iPhone.
If you don’t get Oxford American Writer’s Thesaurus, then don’t worry as you can enable it very easily. All you need to do is a double tap on a word, or long press on a word, choose accordingly if you are reading or editing text. Choose Lookup from the context menu. You will get a page, swipe till the end and locate “Manage Dictionaries”
Note: You can get to these settings by:
Locate Settings icon on the home screen and tap on it. Now tap General and then Dictionary. Check Oxford American Writer’s Thesaurus option is enabled.
Now, if you double tap on a word or do a long press on it, you will get menu tap, Look Up.
You will get a thesaurus option under Dictionary. To access the full list of synonyms, tap on it to expand. You can replace conventional words with fancy ones to decorate your article. It’s an excellent move by Apple to add thesaurus to Look Up tool in iPhones and iPad.
Isn’t it cool to have a thesaurus right on your iPhone? You don’t have to buy a physical, leather bound thick thesaurus dictionary and carry around wherever you go. There are a lot of third-party applications that could solve the purpose but nothing beats a default app. So, with iOS 12, you have thesaurus right in your iPhone.