quasquicentennial
/ˌkwɒskwɪsɛnˈtɛnɪəl/US
noun
A one-hundred-and-twenty-fifth anniversary.
adjective
Of or commemorating a one-hundred-and-twenty-fifth anniversary.
Origin
1960s; earliest use found in The New York Times Book Review. Irregularly from qua- + -squicentennial, the intended sense being ‘a centennial plus a quarter’.