among lawyers, signifies the power a person has, by virtue of his office, to do certain acts without being applied to. Thus a justice of peace may ex officio, at his discretion, take surety of the peace, without complaint made by any person whatsoever.

There was formerly an oath ex officio, whereby a supposed offender was compelled in the ecclesiastical court to confess, accuse, or clear himself of a crime; but this law is repealed.