O’Ca·sey (?-k??s?), Sean Originally John Casey. 1880-1964. Irish playwright. His dramas, including Juno and the Paycock (1924) and The Plough and the Stars (1926), show compassion for the poor and concern over Irish political issues.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.