valedictory

Of or pertaining to a valediction ("an act of parting company; a speech made when parting company"); designed for or suitable to an occasion of bidding farewell or parting company.

“a valedictory oration”

CanadaUSOf or pertaining to a valedictorian ("the individual in a graduating class who delivers the farewell address, often the person who graduates with the highest grades").

Of a speech expressing leave-taking

“a valedictory address”

An address given on an occasion of bidding farewell or parting company.

specifically canadaUSA speech given by a valedictorian at a commencement or graduation ceremony.

A farewell oration (especially one delivered during graduation exercises by an outstanding member of a graduating class)