semicentennial UK /ˌsɛmɪsɛnˈtɛnɪəl/US /ˌsɛˌmaɪsnˈtɛniəl/adjective 1noun 1forms 1 adjective1 •Of or related to a 50th anniversary, occurring every 50 years. noun1 •A 50th anniversary.The city celebrated its semicentennial last year. formssemicentennials
