The word “indenture” is something of an oddity.
Here’s how Black’s Law Dictionary defines it:
A formal written instrument made by two or more parties with different interests, traditionally having the edges serrated, or indented, in a zigzag fashion to reduce the possibility of forgery and to distinguish it from a deed poll.
Obviously we no longer produce contracts with serrated edges. Nevertheless, the word “indenture” has survived in the following terms (again, the definitions are from Black’s Law Dictionary):
bond indenture. 1. A contract between a bond issuer and a bondholder outlining a bond’s face value, interest rate, maturity date, and other features. 2. A mortgage held on specified corporate property to secure payment of the bond.
debenture indenture. An indenture containing obligations not secured by a mortgage or other collateral. • It is a long-term financing vehicle that places the debenture holder in substantially the same position as a bondholder secured by a first mortgage.
trust indenture. A document containing the terms and conditions governing a trustee’s conduct and the trust beneficiaries’ rights.
So “indenture” is simply a synonym of “agreement” and “contract” that has come to be used to refer to a limited group of documents. One could just as well refer to a “bond agreement” or “trust agreement.” If someone felt inclined to do so, I wouldn’t object. The only thing that “indenture” has going for it is tradition, and tradition isn’t a sufficient reason to perpetuate a given usage.
Can you think of another synonym of this sort for “agreement” and “contract”?