To make a stipulation.
To enter into, or promise something by, a covenant.
To enter a formal agreement.
To bind oneself in contract.
A promise, incidental to a deed or contract, either express or implied.
An incidental clause in an agreement.
An agreement to do or not do a particular thing.
A pact or binding agreement between two or more parties.
To make something certain.
To give an assurance that something will be done right.
To assume or take responsibility for a debt or other obligation.
The person to whom a guarantee is made.
A person who gives such a guarantee; a guarantor.
A legal assurance of something, e.g. a security for the fulfillment of an obligation.
More specifically, a written declaration that a certain product will be fit for a purpose and work correctly; a warranty
Anything that assures a certain outcome.