func·tus of·fi·cio /'fəŋk-təs-ə-'fi-shē-ō, 'fu̇ŋk-tu̇s-ȯ-'fē-kē-ō/ adj [Latin, having performed his duty, having served its purpose]: of no further official authority or legal effect
the warrant... had been returned and was functus officio — Cady v. Dombrowski, 413 U.S. 433 (1973)
once an arbitrator makes an award she is functus officio
— used esp. of an officer who is no longer in office or of an instrument that has fulfilled its purpose
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.