The longest word in Shakespeare has 27 letters

Shakespeare coined or popularised over 1,700 words still in common use, including 'bedroom', 'lonely', 'generous', 'obscene', and 'swagger'. His longest word appears in Love's Labour's Lost (Act V, Scene 1): 'honorificabilitudinitatibus' (27 letters) — a grammatical form of a Medieval Latin word meaning 'the state of being able to achieve honours'. It was not original to Shakespeare but was used as a comic showpiece. Shakespeare is credited with using more unique words than any other English author — approximately 31,534 distinct words across his complete works.

Source: Crystal & Crystal, Shakespeare's Words (2002)