The Greek pronoun deina is an indefinite reference meaning 'such a one,' 'a certain person,' or 'so-and-so' — used when referring to an unspecified individual. It appears in Matthew 26:18 where Jesus sends disciples to find 'a certain man' for the Passover preparations.
Jesus' use of deina ('tell the certain man') in directing the Passover preparations reveals His supernatural foreknowledge. The disciples simply follow His instructions and find everything prepared exactly as He predicted. This pattern of divine arrangement — where Jesus sends ahead and things fall into place — previews the resurrection: He always goes before His people, preparing what is needed. The unnamed host becomes an unwitting participant in the Last Supper's eternal significance.