indenture (n.) Look up indenture at
late 14c., endenture, indenture, "written formal contract for services (between master and apprentice, etc.), a deed with mutual covenants," from Anglo-French endenture, Old French endenteure "indentation," from endenter "to notch or dent" (see indent (v.1)).

Such contracts (especially between master craftsmen and apprentices) were written in full identical versions on a sheet of parchment, which was then cut apart in a zigzag, or "notched" line. Each party took one, and the genuineness of a document of indenture could be proved by laying it beside its counterpart.
indenture (v.) Look up indenture at
1650s, "enter into a covenant;" 1670s, "bind by indenture," from indenture (n.). It was used earlier in a sense "to wrinkle, furrow" (1630s). Related: indentured; indenturing.