sesquicentennial

Of or relating to a period of 150 years.

A 150th anniversary or its celebration.

Relating or pertaining to a period of a century and a half; one-hundred-and-fiftieth: as, a sesquicentennial celebration.

A one-hundred-and-fiftieth anniversary.

Occurring every 150 years

Of, or relating to a sesquicentenary

A 150th anniversary.

the 150th anniversary (or the celebration of it)