pledge
Synonym discussion
Sense: verb/1
For this sense, pledge is more formal than promise and often sounds public, official, or tied to support, money, or action. Promise is the normal everyday choice for almost any situation. Vow is stronger and more emotional, often used for deeply felt personal or moral decisions. Commit often focuses on giving yourself fully to a plan or cause, even when no public statement is made. Guarantee is different again: it stresses certainty of a result, not mainly the act of giving your word. A mayor may pledge to rebuild a bridge, a friend may promise to call, and a doctor may guarantee that a machine will work properly.