But this is not about paper. You're asking about online.
\ ˈliv \
right at the top, which answers your question literally. But presumably you want a lot more. For that you really need to look at a word list. Most such extensions, beyond the basic grammatical word endings, are simply found by look at the words alphabetically after the root word.
On-line this is usually not handed to you (you get a page for a word and that's it, you don't have an easy way to look at the alphabetically next page).
So you can look at word lists to see extensions, and then look up their definitions back in the online dictionary.
Of course, the OED, unfortunately behind a paywall, on every page for a word, gives the alphabetical 'neighborhood' where it is easy to see and link to suffixed words.
As to extensions by prefix, this strategy doesn't work at all.