—v.t. 1. to take upon oneself, as a task, performance, etc.; attempt: She undertook the job of answering all the mail. 2. to promise, agree, or obligate oneself (fol. by an infinitive): The married couple undertook to love, honor, and cherish each other. 3. to warrant or guarantee (fol. by a clause): The sponsors undertake that their candidate meets all the requirements. 4. to take in charge; assume the duty of attending to: The lawyer undertook a new case.
—v.i. Archaic.to engage oneself by promise; give a guarantee, or become surety.