The nurse is a servant in the Capulet household and is the former wet nurse of Juliet. She is long-winded and often resorts to low humor of sexual innuendo. She often uses the wrong words in place of the ones that should be used (malapropism--for example, saying that one is amphibious when one means ambidextrous). She chatters mindlessly on almost every occasion where she appears in the play.
While there are many characters who use puns and other plays on words, no other characters come to mind as quickly as the nurse for the use of malapropism as a source of humor in the play.