He introduced around 600 words in Hamlet that he had never used before, two-thirds of which he would never use again

The roughly 4,000 lines in the play [Hamlet] ended up requiring nearly the same number of different words (for comparison’s sake, Marlowe’s Doctor Faustus and The Jew of Malta each use only about half that number). Even the 14,000 or so different words or compounds that Shakespeare had already employed in his plays (by the end of his career that figure would reach about 18,000) proved insufficient. According to Alfred Hart, who painstakingly counted when and how Shakespeare introduced each word into his work, he introduced around 600 words in Hamlet that he had never used before, two-thirds of which he would never use again. This is an extraordinary number (King Lear, with 350, is the only one that comes close; in the spare Julius Caesar only seventy words appear that Shakespeare had not previously used).

J. Shapiro, 1599: A Year in the Life of William Shakespeare (2005), 320