Feast of Corpus Christi

Solemnity of the Most Holy Body and Blood of Our Lord Jesus Christ.

The feast was originally on Thursday after Trinity Sunday and was known in English as "Maundy Thursday."

Online Etymology Dictionary

mid-15c., from M.E. maunde "the Last Supper," also "ceremony of washing the feet," from O.Fr. mandé, from L. mandatum "commandment," in reference to the opening words of the church service for this day, Mandatum novum do vobis, "A new commandment I give unto you" (John xiii.34), words supposedly spoken by Jesus to the Apostles after washing their feet at the Last Supper.