semiquincentennial

/ˌsɛ.miˌkwɪn.sɛnˈtɛ.ni.əl/

Etymology

From semi- (“half”) + quincentennial (“500th anniversary”).

adj

Of or related to a 250th anniversary.

noun

A 250th anniversary.“The year 2026 will mark the semiquincentennial of the founding of the United States.”