semicentennial

Marking the 50th anniversary of an event.

A 50th anniversary or its celebration.

Occurring at the end of, or celebrating the completion of, fifty years, or half a century: as, a semi-centennial celebration.

A semi-centennial celebration.

A fiftieth anniversary.

Of or pertaining to half of a century, or a period of fifty years.

Occurring every 50 years

A 50th anniversary.

of or relating to or marking the 50th anniversary

the 50th anniversary (or the celebration of it)