prom·ise
noun
1.
a declaration or assurance that one will do a particular thing or that a particular thing will happen.

“what happened to all those firm promises of support?”
synonyms: word (of honor), assurance, pledge, vow, guarantee, oath, bond, undertaking, agreement, commitment, contract, covenant
“you broke your promise”

oath
noun
1.
a solemn promise, often invoking a divine witness, regarding one’s future action or behavior.
“they took an oath of allegiance to the king”
synonyms: vow, pledge, sworn statement, promise, avowal, affirmation, word, word of honor, bond, guarantee; formaltroth
“an oath of allegiance”