Terrific. 7 years of single-handed labor he sent to his publisher in 1755 2,300 pages, containing some 43,000 words, some with more than 100 definitions, incorporating for the first-time pronunciation, Greek and/or Roman etymology, and an example of how others had used the word - many from Milton, Shakespeare, Pope, and Jonathan Swift. Although a dozen attempts were made by English lexicographers over the previous century to provide guides to words for academics, nothing came close to Johnson's seminal "Dictionary of the English Language" in depth and breadth.
This is a modern abridged version, of maybe 5,000 of the 'best' examples, of how he covered the words he chose. Takeaways: Shakespeare had no reference guides whatsoever, and none of the Greek & Roman classics had yet to be translated into English, so, too, Cervantes' Don Quixote was just published in Spain and only available in Spanish. So . . . Shakespeare guessed at spellings and meanings, and when needing a word or a phase to mean something that he hadn't yet come across, he made it up . . . lots of new words and phrases, making it necessary that we read him with a guide annotating liberally. Further, many (most?) words from Johnson's time have changed . . . both their spelling and definition.