Dictionary is a useful app that helps you get definitions of the words you don’t know. You don’t even need to copy and paste the unknown words in the Dictionary, as it offers a useful feature called Look Up in Dictionary. All you need is right-click the word and select Look Up in Dictionary from the menu that appears. With just a couple of clicks you’ll get a full meaning of the word, its set of synonyms in Thesaurus, Apple definition if the word relates to Apple, and a Wikipedia article, if applicable.