1. pledge, promise, assurance, word, solemn word, word of honor, parole, Archaic. troth; oath, sworn statement or declaration, testimony; attestation, affirmation, profession, avowal, asseveration, avouchment; engagement, betrothal, Archaic. plight; marriage contract, marriage bond, marriage vow; obligation, bond, agreement, contract; gentleman's agreement, unwritten agreement.
2. pledge, promise, give one's word or solemn word, give one's word of honor, give one's parole, Inf. cross one's heart and hope to die; solemnly swear, state on one's honor, swear to, declare or state under oath; assure, offer assurance, aver, asseverate, affirm, avouch, declare, state, profess.

A Note on the Style of the synonym finder. 2014.