Indenture

[Sarah]

A mutual agreement in writing between two or more parties,whereof each party has usually a counterpart or duplicate; sometimesin the pl., a short form for indentures of apprenticeship, thecontract by which a youth is bound apprentice to a master.The law is the best expositor of the gospel; they are like a pair ofindentures: they answer in every part. C. Leslie.

[Sommer]

(in the past) to officially agree that someone, often a young person, will work for someone else, especially in order to learn a job:

[Dorothey Allen]

A legal agreement, contract, or document.