A free app for Android, by Volcera.

Offline English Dictionary with Synonyms is a free-to-download dictionary app. It supports offline mode and allows you to save your preferred synonyms and word definitions to your Android device. 

This dictionary contains synonyms and word definitions. The synonyms are organized in different categories. You can select any category to browse through the synonyms. It’s very easy to use and can be used as an offline dictionary. There are 2-3 seconds over the translation to share a definition. You can choose to show the definition in an image or speech. The app also allows you to save the definitions in any Android device.

This dictionary supports both English and American English accents. The speech recognition is not perfect, so if you don’t speak English, the app will not work properly.