mid-twentieth

adjective1

1. •
   Usually used before century to indicate the middle part of the 20th century. The term is often used to refer to the events that occurred in the second third of the twentieth century (1934–1967). However, in architecture, preservation, and real estate, it is commonly used to refer to the period from after World War II to the mid-1970s.

   • Since the mid-twentieth century, the exchange of Orders has become less personal and more formal and diplomatic. http://www.royal.gov.uk/output/page4872.asp