Android (rooted): Something that is strangely missing from Android is a system-wide dictionary. You're probably used to highlighting and copying a word, and then pasting it into Google to look it up. XDictionary is an Xposed module that puts word definitions just a couple of taps away.
With the module up and running, select a word you need to look up and tap the Define option in the popup. The module will look up the word on Wiktionary and display the definition for you. The Define option is not compatible with all apps at the moment -- Google Docs is problematic right now, but there are updates in the pipeline, including translation features.