Making it up as he went along................

...Shakespeare  accelerated his pace as his career proceeded.  In plays written during his most productive  and inventive period - Macbeth, Hamlet, Lear - neologisms occur at the fairly astonishing rate of one every two and a half lines.  Hamlet alone gave audiences about six hundred words, that according to all other evidence, they had never heard before.
       Among the words first found in Shakespeare are abstemious, antipathy, critical, frugal, dwindle, extract, horrid, vast, hereditary, excellent, barefaced, assassination, lonely, leapfrog, indistinguishable, well-read, zany, and countless others (including countless).  Where would we be without them?  He was particularly prolific, as David Crystal points out, when it came to attaching un- prefixes to words to make new words that no one had thought of before - unmask, unhand, unlock, untie, unveil, and no fewer that 309 others in a similar vein.  Consider how helplessly prolix the alternatives to any of these terms are and you appreciate how much punch Shakespeare gave English.

-Bill Bryson,  Shakespeare:  The World as Stage