[Latin, From office.] By virtue of the characteristics inherent in the holding of a particular office without the need of specific authorization or appointment.
The phrase ex officio refers to powers that, while not expressly conferred upon an official, are necessarily implied in the office. A judge has ex officio powers of a conservator of the peace.
Law Library - American Law and Legal InformationFree Legal Encyclopedia: Estate for years to Ex proprio motu (ex mero motu)