swear in
swear in or swear into {v.}
To have a person swear or promise to do his duty as a member or an officer of an organization, government department, or similar group. — "Swear into" is used when the name of the group is given.
Mary and Ann will be sworn into the club tonight.
Fred was sworn in as class president.
Many new men were sworn into the army last month.
At the inauguration, the Chief Justice of the Supreme Court swore in the new President.
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Source: A Dictionary of American Idioms