The language at SuttaFriends.org is as simple as possible. Still, there will always be new words we need to learn. When words have a special meaning the the Buddha’s teachings, you will find a dashed underline indicating that the words can be touched or clicked to reveal a definition:
If you want to find suttas that talk about a specific word, you will want to use the topic index or the search.
External Dictionary
For other words, we recommend software called WordWeb. There is a free Windows version, free Android app, and free iOS app. They allow you to select any word on a web page to look up the dictionary.